I'm not sure I have one yet. I beat it on the first two difficulties and been playing "King" lately.
So far I'd say, it varies based on the map and your starting location.
I've had a game where Japan was on an island and teched up all game, while Genghis attacked me for most of it, thereby delaying me from being able to tech up as fast. Japan launched his first space module just as I got tank technology.
So if you are isolated, you can tech up most of the game too.
Another where, I got a Pangea map and all 4 of the other empires declared war on me over a short period of time in the Ancient Era.
It gets annoying when you can't even build your first library, because you are continuously building units to defend your cities and attack stray units.
My location was the problem in that one. I started in the middle and all of the other empires had to do thru me first to get to any contact with the others.
The maps are so small on CivRev too.
When I can't even create the cities around my radius one, 3-4 tiles away from my Capitol without war being declared, the game has issues.
Expand more, build less. Rule of thumb for Civ Rev is that buildings are almost useless and more cities is always better, so beeline for Code of Laws to get into Republic and expand as much as you can before the AI gets uppity. Hammers wasted on building like Libraries are not spent on more settlers, so you generally shouldn't even build them in the first place. Units are more situational but you still only have to build what you need, and not a lick more. Also, learning the art of the horserush will keep you safer than any defense you could ever emplace.
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I love the game so much, I kind of like them all really. I recently got into mainline Civ, specifically Civ4, and this game really makes you appreciate the very subtle differences and advantages most of the civs have. They don't have much of an advantage in terms of magnitude over each other, but as you get better and better at the game and play it on a higher level you learn to really leverage what they do have and milk it for all it's worth.
And then there's the Americans
Most broken civ in the game by far, and throws that whole feeling out of whack.
Anyway, some of my favs:
Mongols: I love the challenge and the dynamics of using them: each game is an adventure when you can't rely on huts. The 3 move horse units are spiffy and I *love* that mountain bonus, it makes for extremely easy production cities in the mid-game Knight spamming era, or one/two mega-production centers that can crank a wonder per turn later on! Only the Americans can really rival that late game production capability.
Japanese: I purposely never leverage the greatest bonus the japanese have, the knight attack, because I'm not much of a warmonger in the mid-game, only extremely early or late after getting tanks, but undeniably that food bonus to water tiles from the outset is amazing. Especially considering how important it is to tech and expand in this game, and how that bonus lets you grow without sacrificing beakers...its amazing, and they are one of the easiest to use because of it. Just expand and make sure you have as much water as possible, and rake in the tech.
Aztecs: The heal bonus is stupidly strong, especially in the early game with horses or warriors. And that free starting 25g lets you settler walk for a couple turns for free basically (you should generally seek to earn a total that equals about 8g per turn you walk, or gain a net move in the direction of an opponent per turn that you walk). Probably the 2nd strongest early game after the Americans, and that's saying something!
Chinese: If the Americans are easy-mode, the Chinese are more like easy-mode Lite. Every bonus they have is awesome: starting with 3 pop cities gives you a significant early game advantage no matter how you slice it (just don't screw it up by making a militia, ouch!), free Writing fast tracks you to CoL, free Literacy means you don't even have to tech it and you can get the 1st research bonus, cheap libraries means they are actually worth building making their science game even better on top of the 2 free techs and almost guaranteed Literacy bonus, and finally they get no anarchy in the later stages of the game which is the only time it's really of any use (after you have multiple situational government to switch between). Oh yeah, and because of the 3 pop starting cities, the Chinese excel at horse rushes too, having more tech power and production than any other civ that early. A really, really good civ, the overall #2 behind the Americans IMO.
Romans: Specifically, I like the cheap wonders. Sure, starting with Republic is great and lets you expand early and everything, but my favorite part comes after 5 techs when I can start building multiple wonders in even small, just fair production spots with only like 6 hammers. With just that small number of production you can build the average 150 hammer wonder in 13 turns as the Romans, meaning you could build many of them concurrently and still finish most or all before the AI could even get one. And then because I like to expand all game, the +1 pop on cities in the modern era means 6 pop cities being plopped down, ready to spit out multiple settlers immediately or get right to work as a contributive member of the empire. Overall a fun, easy civ to play considering the metagame.
Arabs: These guys are my latest addition to the favorites club as I just started realizing just how flexible they are in their aggression. I mean, Fundy is a no-brainer for early game power, but these guys can do anything: warrior rush, horse rush, catapult rush (and very quick too, with free math!), keep using horses long after pikemen come out, and or simply field the most super-powered knights in the game. You can freaking Archer rush with the Arabs! The Arabs are stupidly strong in their aggression, so much so that you can completely ignore the expansion aspect of the metagame entirely and just focus on keeping the cities you conquer or wiping everybody out. Only a couple other civs can boast that and other than the Americans those still require a lot of strategy and a bit of luck to pull off on Deity.
Zulu: I really like how powerful the Zulu's early game is. Gaining advantages in the early game is so impact that it can determine the entire rest of the game and how smoothly (or not) it goes from then on. With 2 move warriors and overruns at 3x power, the Zulu can explore the map and clean up huts and goodies faster than anybody else, even the Americans or Aztecs, and that means you can have your hands on some serious gold and thus extreme power to leverage. Or you could just warrior rush
The overrun bonus comes in handy in a few specific situations later that just make life easier. Namely, vet horse armies overrunning single non-fortified archers or fortified warriors or legion armies is quite handy in keeping things speedy and preventing vulnerability from injuries. They don't have much else to offer beyond this strong opening but they are still fun.
Spanish: Mostly for the Vet Galleon fleet + Legion stacks of doom strategy, which is always shocking in its effectiveness. Other than that, I like the extra gold form exploration, which really adds up if you are playing the way you're supposed to, and starting with Whale access + Galleons is situational but very spiffy if you are lucky enough to leverage them. I also have a soft spot for them because they were my favorite civ when I was learning to play back when I sucked a lot more at the game than I do now
Americans: Of course I couldn't get away without mentioning good ol' USA. The horribly, terribly BROKEN AND OVERPOWERED Americans
. Playing the Americans is a win button even in Deity, there's just nothing that can really be done to stop you once the 5 tech rush bonus kicks in and even then you start with a Great Person which has the potential to vastly improve your starting situation above a more standard civ like Russia. The fastest horse rush in the game, the most powerful unit macro of any civ, all good bonuses but especially the 5 tech and 24 tech ones...these guys are just nuts, and I think that honestly that the only way to can even possibly fathom losing as the American in single player, on any difficulty, is if you intentionally gimp yourself or screw up by being too extremely aggressive before horses or your rush bonus sets in, IN ADDITION to being screwed over by your starting GP by getting a Great Artist/Thinker or Great Leader. Even then, unless you sit there and take it, it would be an uphill battle for the AI to try to cripple you before 5 techs and after 5 techs you could easily break out and overpower them like always.