I do not have a favorite horror "movie", but I really like a scene from "hour of the wolf"(you have the whole movie on YT) when a man is overcame by his "jealousy" (it is unclear) https://www.youtube.com/watch?v=38wuGzmqJkw (go to 1:30)
I would have to say it is a tie between "A Nightmare on Elm Street" or "Queen Of The Damned"...
Hmmm I'd say The Exorcist. The original one, anyway. Not those crap modern reboots.
Exorcist 3 was actually pretty well done, freaky as hell........but i have to go with The Shining
Suspiria, the original one, of course.
Lucio Fulci's - The Beyond
Return of the Living Dead from 1985... gore, humor and a great soundtrack as well.