RE2 for me.
It did everything RE1 did right but improved on it all, aside from maybe being slightly less scary at times. It feels huge, the puzzles are good, Lickers are terrifying and the police station and surrounding facilities gave the game a sort of "monster flick crossed with spy movie" feel to me.
I haven't finished RE3, but I thought Nemesis was more obnoxious than Mr. X and it felt less "survival" than the others.
It's probably still good though, I just haven't formed a real opinion yet.