Both are good UFC has the cash to get any fighter tho plus I think Dana White's matching of fighters produce's much more even, better fights.
It depends if you like the cage, or if you prefer a more traditional way of fighting in a square ring. Both are very similar, the only differences being UFC is English (America mainly) and Pride is in Japan with way less English fighters (but there is English commentary for the Westerners by Frank Trigg and co.). Until the recent takeover from UFC, Pride had a few less rules regarding strikes - you were allowed kicks and stamps to the head when an opponent was on the floor etc etc. Now however, Pride is gonna be playing by the same rules as the UFC but it will still be in a Square ring. Players from both competitions are now able to fight in UFC/Pride too. Good stuff