What do you think is the scariest horror movie?

Can't have this conversation without bringing up The Shining (1980). The atmosphere Kubrick created is truly haunting and it's the type of thing that stays with you long after you stop watching. Jack Nicholson chasing you with an ax isn't exactly pleasant either.

One of my favorite movies ever, Rosemary's Baby (1969) doesn't have any jump scares but also is just plain disturbing and stays with you after it's over as well.

The original IT scared me as a kid, I kept seeing him in the corner of my bedroom.

The Thing '82 scared the heck out of me. It probably helped that I was a kid at the time. Horror movies don't affect me as much today.