Best - Resident Evil 2, 1 was fantastic, but 2 perfected the formula and gave it a stupendious scenario. I always felt like the character could GTFO anytime in the original story and that killed a bit of the mood for me. "Get out of the mansion douchebag! Run you mutha-" etc etc.
The second RE had the character trapped in a whole city full of zombies and that makes the sense of helpless all the more believable. You CAN'T run away because going out into the street is asking to become zombie chowder.
Superb blend of horror, action and puzzle solving.
Worst RE5 - its not RE, I felt like I was playing ZombieGearsofWar with crappy control. =/