Friday The 13th: The Final Chapter, as it's the most 80s of the series. I mean, it's got Feldman and Crispin, for crying out loud!
Halloween: The original... TOTALLY!
A Nightmare On Elm Street : Part 3 - The Dream Warriors, as I feel this is where Freddy's personality really came out. Plus, it's got the best set pieces and FX of the series IMO. Patricia Arquette is pretty cute in it and you just can't beat flippin' DOKKEN playing the theme song!
Saw: Do not care for this series at all, but if I have to pick, it'd be the original. That's pretty much it.
Scream: The original fer sure. It's a fun flick (and series) that reinvigorated the slasher genre at a time when the genre was lagging.
The Texas Chainsaw Massacre: Original. Still frays my nerves to watch it. Still one of the rawest, most visceral horror films ever made despite the lack of on screen gore.
Alien: Aliens. The archetypal 80s sequel: big balls, big guns, big action, more of everything. Kick... ASS!
Predator: 2. Love the original, but I've grown fond of the sequel over the years, due to the city setting and how it expanded on the hunters' mythology.
Phantasm: 2. Like Aliens, it eschews suspense in favor of gratuitous machismo.
Evil Dead: 2. LOVE the original like it's my own child, but this is the one that spawned the most (IMO) iconic ED imagery and made Bruce a cult hero. It wastes no time in blowing your hair back.
Hellraiser: Original. A truly scary, lurid, dangerous feeling piece of mainstream horror film making.
Child's Play: Bride of Chucky. The original is just another killer doll movie for me. This one takes the concept deliriously over the top.
Final Destination: Not a fan of this series either, BUT I like the original, as it was certainly was an original and a good horror film. The sequels are all about the kill scenes and not much else.
I'll add -
Leprechaun (seriously): Not really a fan of this franchise either, BUT I kinda dig the original because it's pretty funny to see Jennifer Aniston in this early role.
Candyman: The original. What a great, spooky urban legend come to nightmarish life thanks to Clive Barker's twisted imagination, the great Tony Todd, and Phillip Glass's creepy score.
Urban Legend: Original. Fun 90s slasher. Both sequels blew.
I Know What You Did... : Original. Another fun post Scream 90s slasher. It's not Cherry Falls, but hey, it's got JLH's boobs. The sequel was standard with Jack Black in it. The 3rd moved into F13 territory... but, not in a good way.
Return of the Living Dead: Original. One of the best zombie movies ever. I like 2 & 3, but SO WISH 4 & 5 did not exist!
Romero's ... of the Dead series: Day. Bleak, brutal, gory, and intense. Holds up the best out of all the films in the series. Not a fan of anything after Land. That sucks, doesn't it?
Prom Night: 2 - Hello, Mary Lou. The original is a lacklustre slasher, but 2 is a totally awesome blend of Carries & ANOES. Fun flick. Revisit it sometime. I like 3 as well. Never seen 4.
Children of the Corn: Original. More of a fan of the cast than the film itself. Parts 2-5 have their moments for bad DTV slashers.
Night of the Demons: 2. Love the original, but it takes a while to take off. 2 ramps up the pace, gore, n' goo, PLUS it's got a young Christine Taylor looking mighty fine.
Re-animator: Original. Still one of the wildest splatstick horrors of all time. Bride gets better with age, and Beyond is surprisingly fun for all it's flaws. Good series overall. Wish they'd do another.
Maniac Cop: Original. It's a pretty decent action-oriented horror. Part 2 isn't bad and 3 is watchable.
How's that for adding more series to the list?