You've already won games?! I'm still trying to get my head around the new rules!
I've only played with Brazil so far, I've got an absurdly high score but city production is quite sluggish, and I'm lagging behind in science now even though I started off awesomely well :/
Ha! This is me. Started a number of games. Closest I had to finishing one was as Siam (picked question mark, rolled as them and went with it). Quit the game at Information Era when I found out I'd end up winning science before culture, even though I was going for culture. Arabia had a crap ton of culture and Byzantium beat me to half the culture wonders by a few turns.
After getting comfortable with trade routes and the new culture game, also with the few experiment games I've played, I can only add this:
Shoshone: Was most excited about, but found out they are not all that great. A very generic Civ like America.
Portugal: May end up being a lot of fun--a surprise since I was least excited about this one pre-release. You can essentially get CS luxuries without the need to pay/keep alliances with them. May actually be a very good naval domination Civ; keep happiness up through Feidora's, keep gold that would have been spent on CS's and use for military instead.
Morocco: Probably one of my favorites so far. I like the color scheme and symbol.
Poland: Meh. Free policies just for playing through the game is great, but otherwise kind of boring.
Haven't played the others yet.