Like many really good movies, the one you remember is the better one from a more recent remake. In this case, my favorite scary movie is actually a tie. Tied between "The Thing" and "In The Mouth Of Madness". I like them for different reasons. I like "The Thing" because it raises questions of doubt and identity and has some really outstanding creature effects. I like "In The Mouth Of Madness" because it lends credence that reality is formed mostly by our agreement-in-perception and that with enough force to change that perception, that you could in a way, change the world.

I find that the complexity of the first is less than the second. Movies like "The Thing" are simple, situated as it is on the premise of failed quarantine while "In The Mouth Of Madness" is actually far more insidious and pervasive and really more scary in the long run.