I was lucky enough to be one of the first people to see Blair Witch, and at that time the hype machine was in overdrive. At the time I was living in the States, and I'd seen the TV 'documentary' about the 'real' events leading up to the creation of the movie out of the recovered videos. At that time, nobody doubted the movie was a true story. I also lived in a remote apartment complex in the middle of acres and acres of wild forest, so that didn't exactly help on the way home after watching the movie. I think it very much depends on the circumstances under which you saw the movie. Unfortunately, by the time it reached the UK it was well known that it was a hoax. It therefore didn't do nearly as well at the box office in this country.
I saw Texas Chainsaw Massacre when I was about 10 years old, again when I was living in the States for a while. Looking back, it was pretty irresponsible of the family I was staying with to allow me to watch the movie, as it seriously scarred me at the time. I might go and see the new one, but it'll probably reduce me to tears!
As for my top five, in no particular order:
1. Halloween (Still creeps me out every time. There's just something unsettling about mental hospitals.)
2. Blair Witch Project
3. Texas Chainsaw Massacre
4. Event Horizon (The subliminal imagery is wicked.)
5. The Ring (The original, not the popcorn-friendly remake.)