The Exorcist hands down. That film is so psychologically damaging when you actually let the story seep through. I saw it when I was thirteen and laughed my head off, I watched it seven years later and was absolutely terrified. Go figure. I'm a person who is very curious and intrigued by the strange, the macabre, the horrific and this tale particularly grabs me each time I dwell and experience it. Sure there are a couple of ridiculous and stupid 'Hollywood' moments which take a lot away from the concentration of an unsettling atmosphere, it's the more subtle moments that create this tension and sense of instability in the viewer's churning mind. I feel sorry for Regan the most, it is such a compelling tale underneath all the terror and the end where you can see that all this poor girl wants to do is hug her mother, that's very poignant.