I definitely think Alien: Isolation is the scariest of them all. Resident Evil 4 is more of an action/adventure game with some scary bits sprinkled in. Only one section really got me spooked, and by that point you've sort of developed some calluses.
I would recommend that RE4 demo. It's a great place to start IMO.
I’ve always been convinced that I’m too wimpy to play scary games, even though I got a decent way through Alien: Isolation.
After hearing rave reviews for the Resident Evil 4 remake, I thought I’d give it a try, and I’m super glad I did. It’s probably one of my top 5 games of all time. I immediately beat it in New Game+, then played the Dead Space remake, and am currently working through RE Village. I’m having an amazing time.