That's tough. I adore OG RE1, RE2, and RE3. Made the PS1 an even better platform. There is also nostalgia, as RE1 was my first horror game and was super scary to me. Also tough, took me months to beat.
But Code Veronica and the Outbreaks, fuck, I loved the Outbreaks. RE4 was amazing, even if I played the crappy PS2 port (didn't own a Gamecube).
It has flaws, but I really like RE5 as well. RE6 can go die in a fire though.
And of course, the re-release of Remake and 0 for this gen, RE7 (great return to survival horror), Remake 2, Remake 3 *chefs kiss*. Rev 2 was pretty good as well.
I answered fifth gen for the poll (that nostalgia), but I honestly love most of the Resident Evil's.