My favorites are REmake and Darkside Chronicles. Remake because, besides being a graphic masterpiece, can give us creeps, and make us think. I really love this game. Darkside Chronicles, not for the original story, but for RE2 and RECV, which i prefer to their original counterparts.
RE2 was my first contact with RE and RECV was the first RE game i completed all alone, so i love both games for their stories, but i prefer their counterparts in DC, because the stories are much more realistic, but still truthfull to the originals (they clear up much of the plot holes).
RE3 is also really cool, but mostly for the city itself and for Nemesis, because the story is a mess up, especially the 2-days break.
RE 4 was fun, but I don't like the new Leon, and Ashley added much more difficulty in the game than all the enemies together (that's why i always chose the Armor outfit, that way i can shoot her as much as i want to).
RE5 was also fun, and beautiful. It was very entertaining and kept a better rythm than previous games, but it don't like these kind of games in which you have to kill all of the enemies with no reason. I prefer those kind of games in which you have to chose between fighting some enemies (if you have ammo/health for it) or taking the longest way, to avoid them.
I also like Dead Aim, which is kind of a transition point between the old and the new gameplay, but still has zombies. The problem with this game is that it is too easy and too short.