i'd say halo 3, but fear 2 looks just as good if not better in some ways. i played fear 1 when i was 11 years old and it scared the crap out of me but it was still a pretty good game.
based on the demo i like fear 2 better 9.5/10 halo 3 is good too 8.9/10 if you have live halo is pretty good but if not fear seems really good im not sure if fear has live