The first two and their remakes are close.
But RE4 to me is a game I often want to replay (and some times do) because I find it so well made in nearly every aspect. And New Game + makes it replay friendly.
Bonus: I'm not sure because I haven't played 7, and this one may be the most similar to 7. But it's giving me some RE4 vibes, and I'm liking the character designs of the vampire ladies so far. And the merchant seems to be another nod to RE4.
Resident Evil 5. It may not be the best game of the series by it's merits, but it's the one I have the fondest memories of them all. I used to play co-op a lot with a special someone whom is no longer a part of my life. All those sleepless nights shooting the crap out of the majinis, damn, I'm getting nostalgic now. I miss those days so much.
The co-op with a friend in RE5 was really fun. Had a lot of memorable sessions with it.
One for example was when my friend failed a quicktime event 10+ times in a row, and it got to the point where I couldn't stop laughing. And when they finally succeeded, I was caught off guard that it was finally my turn to push a button, so I failed as well, and started laughing even more because of it.