As someone wrote before, I quote:
" I am not too sure about Scythia and Sumeria being high tier. In MP maybe. But the thing about is the AI is so incompetent at defending its cities you can build a team of Archers and just as easily take their cities. Basically like this:
- Open with Animal Husbandry (pre-req for Archery), build Slingers
- Research Archery halfway (all the way if you already proced the Eureka)
- Declare war, kill one unit with Slinger (barbarian will do), which completes Archery
- Upgrade all Slingers to Archers at cost of 30 gold each
- Clean house"
I did not try MP, so can't say about that, but above mentioned tactic works in SP on King and Emperor... I was able to conquer early capitals and city states playing different civs. Did not need to use UU at all. I could only argue with first sentece of the quoted text that War Kart is somehow good for scouting and finding good spots for cities.
In my first games I was building scouts, but I abandoned that. They are useless. My build order is slinger slinger/builder slinger slinger/builder (terrain depandant when to build builder) warrior. Then steal settlers, workers, take capitals.
This is the ultimate opening and it is kinda sad an aggresive expansion is favoured so much.
I must say i like Russia. Additional terrain is perfect when racing for spots. Played twice, were my two most perfect starts. Tundra was something found really far

Lavra is extremly superior UD.
Each civ with UD is tier one actually.
I did not play every civ, so for sure my opinion is somehow flawed. Moreover I do not like to "break" the game to myself, so Scythia is good but not as good. Cant understand how people can have fun playing game if they have enough gold to buy everything just because they placetwo cities that produce cavalery all the time? Anyway, each ability that allows "farming" is for me something that is not intended by the game creators and should not be "abused".
I thing that Germany Aztec Japan Rome Russia Sumeria are best. cant tell the order exacly.
update: sorry for all the typos, my langauge help changes words in a wierd manner