tinyE: I thought 2 was way better than one because of the intermingled (spell) story line and the fact that you get to play a face hugger and a chest burster. Let me repeat that: YOU GET TO PLAY A FACE HUGGER AND A CHEST BURSTER!!
Ah. I preferred the 1st one by far. I found it graphically much more creepy, less cartoony, more movies-y. It frightened me more. I also preferred the disjoined sequences of AvP1 (and their feel-the-blank optional storyline) to the more goofy comics plot of AvP2.
Generally, I felt AvP1 was closer to the movies feel, more crual and brutal. And AvP2 was closer to the comics, toys, and other by-products. Plus, I didn't care much for the facehugger/chestburster, as this sequence was too heavily scripted.