What civs are easiest/hardest to play? As far as I can determine, the key factors are civ-specific traits and Unique Units (UU). The manual claims that diplomacy is easier with culturally linked neighbors, but I'm not sure how large a role, if any, that plays, so I am ignoring it.
All of the following are based purely on my opinion. Ive not played all the civs. Im also assuming a high difficulty level (deity or maybe emperor). I'd be interested in hearing others' views.
Easiest:
Iroquois Mounted Warriors are a dominant ancient age force and fully upgradeable all the way to cavalry (useful through most of the Industrial Age). Religious is an awesome trait with cheap temples and one-turn anarchy. Expansionist is marginally useful for early map-selling. The UU advantage is simply huge, though. Only "downsides" are an early GA (but that can lead to lots of early wonders and an early lead, which is never surrendered) and the need for horses for the UU.
Aztecs Some would disagree but their UU is just so awesome. Early retreat, extremely cheap, lots of early leaders make these little guys way cool. Pillaging at speed. Add in militaristic and they promote and crank out leaders. Religious is almost too much to add. The lack of upgrade path for jaguar warriors and the incredibly early GA are the detriments.
Japanese Samurai are both the best offensive and defensive unit for a reasonable period. They prevent retreat, defend as well as musketmen (their contemporaries), only cost 10 shields more, and attack well. Militaristic and religious (again) for leaders and some happy culture. Start with "The Wheel" so can see horses early. Downside is that you have to wait for Military Tradition to upgrade those horsemen you have running around.
Still Easy:
Egyptians War Chariots are essentially horsemen without horseback riding. Very early move 2 with reasonable offense and upgrade directly to knights. Religious and industrious work well. Cheap culture/happiness and lots of improvements from fast workers. Downside is the very early GA and a struggle with mountainous/jungle-infested maps.
Zulu Hate having your horsemen attacked after they do their stuff? Me, too. The answer is the Impi, who is able to keep up. Horsemen don't retreat from these guys, either. Upgradeable all the way to Mobile Infantry. They don't need a resource to build. Their Militaristic nature makes for veteran impi/horsemen hordes and early GLs. Expansionist helps them know where to attack and gives map selling options but is generally weak. Again, an early GA is the downside, as well as the generally weak expansionist trait. Also, culture can be a problem for the Zulus as everything is full price for them and they have no shield bonuses.
Persians The highest offensive number before knights belongs to the immortal, Persia's UU. Still, I find I like legionaries better. I ranked Persia as 'easier' than Rome, though, for a number of reasons. One, Persia starts only one advance away from iron working, since it starts with bronze working. Industrious workers make getting a road to those enemies a lot easier. Scientific is nice, with both cheap libraries/universities and those three free scientific advances. Downside is that the UU can't retreat, leading to high casualties (although an ancient army of three immortals is pretty invincible). The UU also doesn't upgrade, leading to obsolescence problems.
About average:
Greeks Hoplite is an awesome defensive unit up until riflemen (cost compare with musketmen and I know which Id rather have). It upgrades all the way to mech infantry, too, which is nice. Commercial and scientific should lead to huge tech leads, but it doesnt seem to any more than any other civilization. Starting on the road to the Great Library is nice, but science shouldnt be the Greeks problem. Downside is no good offense, hoplites are too slow to really escort horsemen, and the early GA has very little going for it.
Chinese Riders get an extra movement point. Since railroad is still quite a ways off, this gives significantly faster response to invasions and a faster invasion force. The ZOC is nice on paper but is less significant in practice. On the other hand, they fight like knights, I dont think they can run from knights, and cant be upgraded to. Industrious and militaristic make a nice combination, as wars run smoothly and infrastructure on the land is quickly and easily replaced. The GA is perfectly timed for all those nice Middle Age wonders (Sistine, Bach, even Leonardo and Sun Tzu). The inability to upgrade horsemen is a big problem, as are the long periods of anarchy. China is often at war and hence will occasionally lag technologically.
Babylonians Bowmen are a combination spearman/archer. They are a nice shock troop in the ancient age, doing two roles, but their upgrade path stinks. They trigger an early GA which is probably not needed. On the other hand, the twin traits of scientific and religious make the Babylonians the undisputed culture king of Civ3. They have lots of cheap city improvements and should be good at cultural absorption and minimizing flips after conquest. The free tech can be very handy, too. The biggest downside is the adequate but horribly unupgradeable UU. Who needs longbowmen?
Romans Legionaries can, indeed, rule the Ancient Age. At 3/3, theyre the best defenders around (until musketmen, who arent much better and a lot more expensive). They are slow on the attack and no better than swordsmen that way. They also have no upgrade path and require iron. Militaristic is nice for getting elite legionaries and leaders, but legionaries do die a lot more than fast units, since they cant retreat. Commercial is rarely helpful. The Romans other downside is a huge difficulty building cultural improvements, as they have no extra shields and everything is full cost.
Getting Difficult:
Germans Panzers are nice, the extra move and blitzkrieg ability make them terrors of the late industrial age. On the other hand, modern armor isnt that far away, they still really struggle against mech infantry, tanks will still crush them, and panzers come too late in the game to really matter. By that point, a game is usually won or lost and panzers rarely make the difference. The GA really comes at a pretty inconvenient time, as few wonders still need to be built and war is a LONG process. Militaristic is OK, but its had to completely take advantage of early, when its most important. Scientific helps get to tanks a tiny bit faster, but it also serves to shorten the time until modern armor. A very late GA is probably not going to help, the extra movement point isnt enough with RR everywhere, and a short period for a UU make the Germans kind of tough to win with.
Indians War Elephants are nice if you have no iron or no horses, but if youre in that situation, you probably have more problems than just getting knights will solve. Elephants crimp the upgrade path for horsemen, too, for little/no additional merit. At least the Indians are religious, which can solve a lot of problems. Commercial helps some with gold, which will be sorely needed. The GA comes at a great time, for building those Middle Ages wonders, but with no other helps, its a tough climb.
French Musketeers are weird, in that their primarily ability is that you get to keep building a superior older unit (pikemen). For the same shield cost, two pikemen provide much better defense and can upgrade to two good units. Musketeers have better offense than musketmen but are still basically worthless, except to trigger a GA. The French GA is also in a pretty sweet spot for wonders and getting a lead on the AI. Industrious and commercial traits encourage the French to have big cities to get their bonuses. They can also afford a slightly larger empire, with the commercial trait. How they get that empire is a mystery to me.
Hardest:
English Man-O-War is an updated frigate that has a little better attack/bombard values. They can sometimes sink ironclads, but the age of sail is so short. And Magnetism doesnt lead to a particularly valuable GA, other than the fact that it comes late. If you need coal, you can leverage your GA into an attack, but thats not terribly realistic. Expansionist and commercial the British may be, but that is hardly an advantage, as they have no culture benefits, no shield benefits, and a world map only has value so long.
Americans The F-15 comes extremely late, is better at bombard only than a jet fighter (why not use a bomber?), and requires special resources. The very late GA is probably too little too late to save a player thats behind and unnecessary for one thats ahead (one could build the SS faster, I suppose, but tech is usually more important than shields. To get the late GA, you need to start a war and thats a pain on tech.) Expansionist and industrious isnt much better than the British situation. The industrious workers and shields help a little, but the poor UU is a lot to overcome. It breaks an upgrade path, too, to add insult.
Russians The Cossack is the only UU I wish I could simply remove. It breaks the horsemen/knight upgrade path, which is horribly painful. Its only marginally useful, as defense for a fast offensive unit usually is. You have to build all of them from the ground up, theyre barely better than cavalry, cant upgrade, and put a GA in an odd time slot. NO THANKS! Add in questionable value in expansionist, and the scientific trait cant bring them up. The main offensive thread is completely disrupted and knights hang around way too long. Its a huge hurdle with no reward for leaping it.
Arathorn
All of the following are based purely on my opinion. Ive not played all the civs. Im also assuming a high difficulty level (deity or maybe emperor). I'd be interested in hearing others' views.
Easiest:
Iroquois Mounted Warriors are a dominant ancient age force and fully upgradeable all the way to cavalry (useful through most of the Industrial Age). Religious is an awesome trait with cheap temples and one-turn anarchy. Expansionist is marginally useful for early map-selling. The UU advantage is simply huge, though. Only "downsides" are an early GA (but that can lead to lots of early wonders and an early lead, which is never surrendered) and the need for horses for the UU.
Aztecs Some would disagree but their UU is just so awesome. Early retreat, extremely cheap, lots of early leaders make these little guys way cool. Pillaging at speed. Add in militaristic and they promote and crank out leaders. Religious is almost too much to add. The lack of upgrade path for jaguar warriors and the incredibly early GA are the detriments.
Japanese Samurai are both the best offensive and defensive unit for a reasonable period. They prevent retreat, defend as well as musketmen (their contemporaries), only cost 10 shields more, and attack well. Militaristic and religious (again) for leaders and some happy culture. Start with "The Wheel" so can see horses early. Downside is that you have to wait for Military Tradition to upgrade those horsemen you have running around.
Still Easy:
Egyptians War Chariots are essentially horsemen without horseback riding. Very early move 2 with reasonable offense and upgrade directly to knights. Religious and industrious work well. Cheap culture/happiness and lots of improvements from fast workers. Downside is the very early GA and a struggle with mountainous/jungle-infested maps.
Zulu Hate having your horsemen attacked after they do their stuff? Me, too. The answer is the Impi, who is able to keep up. Horsemen don't retreat from these guys, either. Upgradeable all the way to Mobile Infantry. They don't need a resource to build. Their Militaristic nature makes for veteran impi/horsemen hordes and early GLs. Expansionist helps them know where to attack and gives map selling options but is generally weak. Again, an early GA is the downside, as well as the generally weak expansionist trait. Also, culture can be a problem for the Zulus as everything is full price for them and they have no shield bonuses.
Persians The highest offensive number before knights belongs to the immortal, Persia's UU. Still, I find I like legionaries better. I ranked Persia as 'easier' than Rome, though, for a number of reasons. One, Persia starts only one advance away from iron working, since it starts with bronze working. Industrious workers make getting a road to those enemies a lot easier. Scientific is nice, with both cheap libraries/universities and those three free scientific advances. Downside is that the UU can't retreat, leading to high casualties (although an ancient army of three immortals is pretty invincible). The UU also doesn't upgrade, leading to obsolescence problems.
About average:
Greeks Hoplite is an awesome defensive unit up until riflemen (cost compare with musketmen and I know which Id rather have). It upgrades all the way to mech infantry, too, which is nice. Commercial and scientific should lead to huge tech leads, but it doesnt seem to any more than any other civilization. Starting on the road to the Great Library is nice, but science shouldnt be the Greeks problem. Downside is no good offense, hoplites are too slow to really escort horsemen, and the early GA has very little going for it.
Chinese Riders get an extra movement point. Since railroad is still quite a ways off, this gives significantly faster response to invasions and a faster invasion force. The ZOC is nice on paper but is less significant in practice. On the other hand, they fight like knights, I dont think they can run from knights, and cant be upgraded to. Industrious and militaristic make a nice combination, as wars run smoothly and infrastructure on the land is quickly and easily replaced. The GA is perfectly timed for all those nice Middle Age wonders (Sistine, Bach, even Leonardo and Sun Tzu). The inability to upgrade horsemen is a big problem, as are the long periods of anarchy. China is often at war and hence will occasionally lag technologically.
Babylonians Bowmen are a combination spearman/archer. They are a nice shock troop in the ancient age, doing two roles, but their upgrade path stinks. They trigger an early GA which is probably not needed. On the other hand, the twin traits of scientific and religious make the Babylonians the undisputed culture king of Civ3. They have lots of cheap city improvements and should be good at cultural absorption and minimizing flips after conquest. The free tech can be very handy, too. The biggest downside is the adequate but horribly unupgradeable UU. Who needs longbowmen?
Romans Legionaries can, indeed, rule the Ancient Age. At 3/3, theyre the best defenders around (until musketmen, who arent much better and a lot more expensive). They are slow on the attack and no better than swordsmen that way. They also have no upgrade path and require iron. Militaristic is nice for getting elite legionaries and leaders, but legionaries do die a lot more than fast units, since they cant retreat. Commercial is rarely helpful. The Romans other downside is a huge difficulty building cultural improvements, as they have no extra shields and everything is full cost.
Getting Difficult:
Germans Panzers are nice, the extra move and blitzkrieg ability make them terrors of the late industrial age. On the other hand, modern armor isnt that far away, they still really struggle against mech infantry, tanks will still crush them, and panzers come too late in the game to really matter. By that point, a game is usually won or lost and panzers rarely make the difference. The GA really comes at a pretty inconvenient time, as few wonders still need to be built and war is a LONG process. Militaristic is OK, but its had to completely take advantage of early, when its most important. Scientific helps get to tanks a tiny bit faster, but it also serves to shorten the time until modern armor. A very late GA is probably not going to help, the extra movement point isnt enough with RR everywhere, and a short period for a UU make the Germans kind of tough to win with.
Indians War Elephants are nice if you have no iron or no horses, but if youre in that situation, you probably have more problems than just getting knights will solve. Elephants crimp the upgrade path for horsemen, too, for little/no additional merit. At least the Indians are religious, which can solve a lot of problems. Commercial helps some with gold, which will be sorely needed. The GA comes at a great time, for building those Middle Ages wonders, but with no other helps, its a tough climb.
French Musketeers are weird, in that their primarily ability is that you get to keep building a superior older unit (pikemen). For the same shield cost, two pikemen provide much better defense and can upgrade to two good units. Musketeers have better offense than musketmen but are still basically worthless, except to trigger a GA. The French GA is also in a pretty sweet spot for wonders and getting a lead on the AI. Industrious and commercial traits encourage the French to have big cities to get their bonuses. They can also afford a slightly larger empire, with the commercial trait. How they get that empire is a mystery to me.
Hardest:
English Man-O-War is an updated frigate that has a little better attack/bombard values. They can sometimes sink ironclads, but the age of sail is so short. And Magnetism doesnt lead to a particularly valuable GA, other than the fact that it comes late. If you need coal, you can leverage your GA into an attack, but thats not terribly realistic. Expansionist and commercial the British may be, but that is hardly an advantage, as they have no culture benefits, no shield benefits, and a world map only has value so long.
Americans The F-15 comes extremely late, is better at bombard only than a jet fighter (why not use a bomber?), and requires special resources. The very late GA is probably too little too late to save a player thats behind and unnecessary for one thats ahead (one could build the SS faster, I suppose, but tech is usually more important than shields. To get the late GA, you need to start a war and thats a pain on tech.) Expansionist and industrious isnt much better than the British situation. The industrious workers and shields help a little, but the poor UU is a lot to overcome. It breaks an upgrade path, too, to add insult.
Russians The Cossack is the only UU I wish I could simply remove. It breaks the horsemen/knight upgrade path, which is horribly painful. Its only marginally useful, as defense for a fast offensive unit usually is. You have to build all of them from the ground up, theyre barely better than cavalry, cant upgrade, and put a GA in an odd time slot. NO THANKS! Add in questionable value in expansionist, and the scientific trait cant bring them up. The main offensive thread is completely disrupted and knights hang around way too long. Its a huge hurdle with no reward for leaping it.
Arathorn