Worst one ever you ask? The Exorcist II: The Heretic. Oh my god. I almost fell asleep during it. Ridiculous. Though Linda Blair was cute.
Best? Surely not Exorcist...that belongs on the comedy channel. The Shining was funny too. Clearly its a generation thing.
As far as scary: Session 9, Exorcist: Beginning, Saw, 28 Days Later, The Amityville Horror (remake) and The Dark Hours scared me alright.
Whats on your best/worst list?