Okay, putting personal biases aside, I'll have to say Code Veronica. While I absolutely love 1-CVX with every fiber of my being, in terms of scares, length, difficulty, game-play, story and character depth, Code Veronica gets the vote. The sheer brilliance of having Alexia and Alfred go toe-to-toe with our favorite Redfield's was just amazing; it set up a dynamic that no other partnership could have. And I also have to say that Alexia is probably one of the, if not the, best Resident Evil villains - she's just that hardcore.
And here come the piranha's...