It's China vs. Japan obviously.
UP: Japan > China. Both awesome, but Japan's UP is one of the most overpowered in this game and makes them truly invincible. China's UP is less visible and becomes a plain tech rate boost after a while in Human hands.
UB: China > Japan. China's UB is actually real, and has a real and important effect on game play. Neither can be said of Japan's UB.
UU: China = Japan. Both are there mostly for flavor (and they are both good for this purpose), as neither civ needs a UU at all for different reasons.
UHVs: China > Japan. Japan has 1 interesting UHV, the expansion one. The other 2 UHVs are time wasters, nothing more (especially "first to finish tech tree - ewww"). All 3 of China's UHVs are balanced and yet challenging.
Vote goes to China. IMO the definitive 3000BC civ along with Rome.