Generally speaking, I still haven't played with the mongols, which is weird. There just always seems to be a better choice. BNW civs only, I'm gonna get stick for this, but I'm not a fan of Venice. I just finished a game with them on emperor and the last 50 turns were just waiting for the diplo victory. The amount of money they get is ridiculous, but after settling your base and allying with every city state on the map, spreading my religion across the whole world and establishing world religion and ideology, I literally ran out of things to do and was just clicking next turn for the last 2 hours of the game....