Never played Civ V, but during those countless all-nighters playing Civ IV, I did like playing as the US. Partly because I'm American and it's fun to put the Kremlin in Boston, but also because the Navy SEAL was such a badass, destructive Unique Unit.

On the flipside, it was always fun to play as Mao and put the Statue of Liberty in Beijing. I also played Mongolia alot, because the Keshik was incredible.