Friday The 13th - Part 4, though part 6 is a close second. Part 2: boring. Part 3: my third favorite, mostly for the imaginative effects (eye's-a-poppin!) and a tighter-than-most storyline (horrid segment where the chick relates her "Jason almost got me" story, though). Part 5: for nostalgic reasons, I enjoy it more than most. Part 7: meh. Part 8: crap. Jason Goes to Hell: better than I expected but still far from great. Jason vs Freddy: meh, too. Friday remake: thought it was a slap in the face to even the passive Friday fan. It's suckitude actually angered me.
Halloween - Carpenter's original, hands down, by far, no question about it. Part 2 was merely a clone of the very movies which attempted to clone the original, part 4 was a good try, part 5 was shit, part 6 was double shit, I thought H2O was the best sequel since the original, and I can't count the ways I abhored part 8. "Happy Halloween, motherfucker!" *karate kick* Pure, unfettered dog shit. I do think part 3 is a solid stand alone flick, though it doesn't get a lot of praise. Zombie's remake: very good, and much better than I thought it would be. Zombie's H2: junk without a single saving grace. I was hugely disappointed with it.
A Nightmare On Elm Street - the first is the best, but I have a lot of love for part 2 and part 3 is easily the most imaginative. The rest: pfffft. Except for New Nightmare, which had some interesting ideas. The remake: I laughed through most of it, and not in a good way. Jackie Earl Haley, a good and capable actor, did what he could as Freddy but it was the film equivalent of polishing a turd.
Saw - the first. Saw 2 was basically Cube dumbed down. Part 3 played like a gorier than most but equally insipid SyFy flick. Didn't bother wasting my time with any past that.
Scream - the first. Part 2 was better than I expected. Part 3 blew dog. Part 4 was been there, done that.
The Texas Chainsaw Massacre - the original. I also really like part 2. TCM 3 was a total dog. The remake and its sequels/prequels: undiluted shit.
Alien - the original. Didn't care much for Aliens, thought it was one big exercise in overkill. Part 3 is better than most folks make it out to be. Part 4 is exactly as mediocre as most folks make it out to be, though the FX are top-notch.
Predator - the first. Predator 2 was a joke; the Alien vs Predator movies are tepid crap. I did enjoy Predators, but thought it could (and should) have been better.
Phantasm - part 2. I'm not a big fan of the loopy, nonsensical original, and I've not seen 3 or 4.
Evil Dead - I'd rate the first two about even as they're both effective for what they're each supposed to be. AOD is a fun distraction, but I don't consider it a horror movie by any stretch.
Hellraiser - the first one. Parts 2 and 3 had their moments. Cool female Cenobite in part 4 but that was the best thing about it. Didn't bother with any installments beyond that.
Child's Play - the first one. Child's Play 2 was junk. Child's Play 3 was even worse. I despised Bride of Chucky and didn't bother with Seed of Chucky.
Final Destination - part 2, which I thought was leaps and bounds better than the first. Watched half of part 3 before I got tired of it, and haven't bothered with any of the others.