1. Nightmare on Elm St Franchise - The original Nightmare on Elm St never gets old.  Nightmare on Elm St. Dream Warriors is written co-written by Craven, Chuck Russel(the Mask, Eraser, The Blob), Frank Darabont who Directed Shawshank and the first episode of Walking Dead.  The only film of that series I just CANT watch is Dream Child.  The first half of Dream Masters is awesome as an 80s teen comedy/horror movie, but it really falls off second half.  New Nightmare of course is very solid as well, and was sort of Craven's practice run before Scream.

Scream Franchise - The first film is just so damn great in every way.  I am also a pretty darn big fan of the 4th.  I know it isn't a GREAT film but it is definitely one of my favorites considering all the hot tail running around the whole film..

Halloween - Mainly just the first 2 films here, but the Curse of Michael Myers, and even the ones they show year after year are sometimes watchable.  Oh and Halloween 3 is actually a fun watch as well, and better than most the other sequels.  Halloween 1, 2, and 3 is a pretty damn good trilogy right there.  I've never looked at it that way but really Carpenter made a trilogy of Halloween films because he basically ended up directing the second after the original director handed Carpenter a piece of film.  fThen Carpenter of course produced and scored the 3rd film..

Romero's Dead Franchise - all three films just different and great in their own way..and Day of the Dead being just about the best fucking Zombie movie ever made.

Had to do 4.

^^ Oh I have tremendous love for Hammer's Dracula and Frankenstein films as well as Corman's Poe movies. Aside from the Halloween series, I probably watch those films more often than anything else. I suppose I wasn't thinking of them using the term "franchise" though.

good girl Ms G ! i  love all those as well and i too wouldn't include them as a franchaise xx

Romero's Dead
Saw
Scream
Halloween

Props to Final Destination, F13, and NOES also, I love those films. I adore series films, I love how they develop and you get to know the characters

These are the only two that come to mind which don't include any weak entries.  Every other horror franchise I can think of has had at least one or more shitty installments, who while I may be a fan of certain films in a franchise, I'm not a fan of their franchises on the whole.

Friday the 13th (Jason is just so badass, even if some of the movies stink)

Evil Dead (waaaayyyy too much fun)

1. George Romero's original zombie trilogy
2. Universal's Frankenstein
3. Evil Dead

Halloween
TCM
Saw

But I also love the NOES series, Friday the 13th and Texas Chainsaw (even the next generation as a guilty pleasure) other than Halloween and Saw series they are all pretty tied.