There's elements of many I like depending on my mood; England entirely because of Longbowmen. They're basically Artillery, at a point when it's hilariously unfair.
Germany has those Landsknects. I live in terror of the game ruining potential of those. Everyone hits Civil Service and Bismarck goes nuts. Unless he's me, in which case he goes only slightly loopy.
I used to like France for that +2 Culture before Steam, but my love for them has entirely disappeared because of...
SONGHAI! Oh my God these guys are awesome. I get 270 gold for every Barbarian Camp I burn down, and don't pay upkeep on a temple that has +2 extra Culture (screw you France, this +2 is FOREVER!). I'm absolutely minted and powering through culture! Haaaaaaaahahahahahaha!
Anyway....
I also rock China, because the Paper Maker is another obscenely overdone building. I end up with money coming out of my ears yet again (I like expanding a lot) from a building I'll throw up in every city anyway. Chu-Ko-Nu are just an incredibly amusing bonus.
I'll give a tiny bit of notice to the Greeks. That Hellenic League bonus is way more powerful than it looked. You don't even have to bother with Patronage, but if you do, it becomes utterly, utterly, utterly trivial to keep City States. Even early in the game you can have as many as you can find as Allies, simply because their relations with you barely degrade at all.
Haven't tried the Egyptians. I should really, extra happy from Burial Tombs and obscene Wonder spam sounds tasty.