In my opinion, Financial and organized are the best traits on emperor and immortal level because commerce is usually the bottleneck. Organized is the best of the two because it also provides building bonussen on two essential buildings:courthouse and lighthouse.The dike is in my opinion the best unique building closely followed by the feitoria and the rathaus.
Darius is the best leader combining financial and organized.
Agressive/protective: - I usually specialize one city in building military units so I do not need the extra promotions in ALL cities.
Creative: - culture is less important.
Industrious: -/+ wonders are less important,except national wonders.
Philosophical:-/+ handy in the beginning however GP-production levels off quickly. University bonus is nice
Spiritual:-/+ handy but a good player avoids switching civics too much.
Charismatic:-/+ looks very good on paper still there are enough ways to avoid unhappy people for an experienced player. Experience bonus:I usually specialize one city in building military units so I do not need the extra promotions.
Imperialistic: - handy in the beginning however GG-production levels off quickly,settler building is only important in the very beginning.
Expansive:+ good civic after organized and financial the best: harbor and granary are essential buildings for every city and health is important for quickly building an empire.
So I would chose Darius of the Dutch,Portugues,HRE.
Mehmed II with expansive,organized is second choice and Pacal 2
third with financial,expansive.
Down under my explanation why commerce is the bottleneck and how I adjusted my playing style to this.
For the higher difficulty levels( emperor and immortal, deity is crazy) at random settings without having to dependent on luck space victory is by far the easiest.
Cultural victory is also very easy at random settings but luck is needed since your civilization will lack a big modern army to defend itself. Also I dislike cultural because it is unbalanced and simplistic(you only need three cities and have to pump up the culture slider and than build a large but obsolete army to defend these three cities).
Domination,conquest is impossible without extreme luck because capturing and especially holding cities takes a lot of time because of the exponential strain war and captured cities puts on your gold, even if you are succesful you risk being defeated by weaker civilizations who win by cultural or space victory. If you win domination or conquest on emperor and immortal at random maps you must be a very good Civ 4 player.
SPACE VICTORY GUIDE on immortal/emperor
To acquire space victory teching and a large empire to quickly built the spaceship is essential. For teching AND to sustain a large empire gold is needed, so in my opinion gold is the bottleneck on emperor and immortal.
Om emperor I have won with most leaders by focussing on teching and citybuilding while maintaining a small but strong modern army and navy(strong enough to defend and deter aggressive leaders) . Teching order is ofcourse dependent on the resources available and the maps(water, no water) etc.
Alphabet,pottery, bronze working,mathematics are essential for early and sustained teching: Chop the woods,build cottages on them an build research in your cities. Alphabet is the most important! Consider masonry if stone is near and you have a good chance of building the piramids. Still piramids will mean long term benefit but you risk bad early development.
In general I do not build world wonders ( takes too much time,timing of building is forced upon you)
Only exception is the Three Gorges (I reserve usually one or two engineers for this one, needs river tile city). National wonders are much better since the timing of building is free. Oxford,Moai statues,Heroic epic,Wallstreet are my favorites.
Citybuilding(everycity,library,observatory,university,lab,factory,forge,bank).
Every other building is optional depending on the specific game. Altough I stated that gold is essential I usually focus on building in the following order science,production,commerce etc. I usually build 8 cities.
Capital is the science city (build Oxford and National Park,Academy) and produces research if no important building orders are available.
I have one production city(Military Academy,drydock, barracks,Heroic epic,Moai statues or Ironworks,build mines no windmills here) for all purpose unit building. One commercial city(cottages,Wallstreet!, ALL commercial buildings here, corporations optional if circumstances right:Sid's Sushi is the best) build ONLY wealth here most of the time.
The other cities are minor science and secondary production cities and the city furthest from the capital but still central in the empire has a forbidden palace(therefore I build 8 cities). In general I prefer building cottages, a Town can become a Farm in one turn, however a Farm will take forever to become a Town. Also commerce is more important than food.
Military units:build not to much units(stay below the upkeep for units delete warriors,archers but upgrade less costly upgrades rifleman>infantry) and keep them modern. Remember your military is primarily for self defense not for conquest. Build in one production city for maximum promotions and buidling speed. Expand and modernize your military if diplomacy is souring,sometimes this prevents war. City defending gets the highest priority so build city garrison units with the garrison promotions. Navy is important to protect vital sea resources.Get oil! Even if its means travelling all over the world.
Focus on battleships they do collateral damage.
Civics order is dependent on the specific game.
In general very early:none at all, unless spiritual leader.
Slavery is not an option.
Early/mid game organize building (if religion has spread),mercantilism,constitution,bureaucracy,serfdom.
Free market is sometimes better than mercantilism.
Mid to late:constitution, bureaucracy,enviromentalism,emancipation,free religion. Free speech(+2 gold town) is good but bureacracy is better if you have a big capital and still small minor cities. Count your towns in your minor cities there is a turnover point!
State property really is not necessary with 8 cities and a strategically placed forbidden palace. Also enviromentalism is absolutely necessary for big cities and the windmill bonus rules.
Late to very late universal suffrage(build cottages!), free speech(build cottages!),enviromentalism(build windmills!),emancipation,free religion.
I recently won a space victory with Darius of the Persians on immortal at 1952BC(random settings). I started on an Island and build 8 cities, at the time I came into contact with other civilizations(7) I was last in score and science but had most science and production buildings in all cities. By clever downtrading(only trade with the lowest score civ) and avoiding uptrading(trading with the most powerful civs) and science at 80-90% I slowly gained scientific dominance and climbed the score tree. While keeping a small but strong army and navy.
At 1900 I was second in score but Toetanchamon(first) was bound for a cultural victory. Every Civ was Friendly or pleased with me, I had avoided war by using a generous trading policy and neutral stance on all policies. At around 1910 I razed in a Blitzkrieg using my modern mobile army(modern armor) and navy the two most cultured cities of Toetanchamon. Although Toetanchamon's army was much larger, because of me razing his two strongest cities, and threatening others I forced him to seal a peace treaty. This gave me time to to build the spaceship.
Khmer leader, I presume? (I also refer to him as Survivorman 
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