I'd say REmake and RE4 are a good place to start. After that, hit up 2-3 but I wouldn't recommend the GC ports as stated already, they're insanely pricey and not really worth those prices (they didn't get a complete facelift like the first game did). After that, if you like the games, check out Zero and Code Veronica. I'm not sure why Zero gets a lot of slack, if anything the partner setup completely destroys RE5's way of doing it... but hey, RE5 just sucked. That's for another discussion.
Code Veronica wasn't my favorite, but had some of the toughest puzzles in the entire series I'd say for sure. One of the longer ones too.
I'm going to be honest and say I marathonned the games a few years ago completely backwards, intentionally (since they're just loosely connected and star different characters anyways), I honestly thought it made for a cool experience. Haha, recommended to those who play these a lot if you want a new experience or something I guess!
I honestly don't think I could pick a favorite, they each have their own merits and RE1-RE4 are just pure gold in my book.


