That's a really tough (and interesting) question. I'll go with:
1)
Hellraiser
The first two films are pretty good, and then it goes to trash quickly, but the films are still kind of fun b-movies.
2)
Phantasm
There's really no good film in this franchise, but 1 through 4 are all crazy enough to be fun on rewatch. 5 must be avoided.
3)
A Nightmare on Elm Street
Can't agree with
@KallioWeHardlyKnewYe trashing part 2, as I think 4 and 5 are worse, and 6 is absolute trash, but otherwise he's right, 2 very good films in this type of franchise is pretty good.
4)
Evil Dead
It's only 3 films and a remake, but they're all a lot of fun. In terms of quality, should be top-3 behind the Argento and Romero films.
5) Fulci's Gates of Hell trilogy
Not for everyone. The second film is pretty good, the other two are fun.
6)
Halloween /
Friday the 13th
I'm not a big fan of the first Halloween, but I really like parts 2 and 3. After that it goes nowhere fast, and the mixed timelines starting with H20 (trash, especially its sequel) and the 2018 rebooth (better) don't help much. I like the Zombie remakes. Toss up here with the F13 franchise, where most of the films are more fun (except the terrible remake), but it's just so dumb.
7) The Romero living dead films
In terms of quality, put that on top of the list. You might want to limit yourself to the original trilogy, as the drop is steep after that, but these three first films rank individually very highly here.
8) Argento's The Three Mothers
These films are rarely seen together, but they should.
Suspiria is a rare mix of beautiful aesthetics and horror efficiency (and the remake is great as well), and
Inferno is too a very interesting film, even if lesser known. The third entry is a weaker link, but these first two are must-watch. Like the Romero films, they're very good, and super fun to rewatch too, but more demanding so maybe less appropriate for a binge.
edit: 9)
Re-Animator
Just read
@KallioWeHardlyKnewYe 's suggestion for the Gordon films (and yes, if it counts, that's #1!), and I'm adding this here at nine - first 2 films are great fun, third one is terrible.
10)
Amityville
I think part 1 is an ok film, and part 3 has only one great scene, but I adore part 2. The problem is that everything that comes after that is unwatchable. Any film can put "Amityville" in their title, and some of the latest entries will only make you wish for a quick death - even a painful one would be better than some of these turds. Just stop at 3 and it's a fun franchise.
11)
The Exorcist
Just watched them all again recently. The films really don't work well together. 1 and 3 are very good, and should be considered a pair. The others can all be forgotten, it's like they didn't understand the first film.
I wish I could put some of the more recent franchises, but none of them really hooked me up. I'll see what others recommend and might give one another shot. I'm sure I'm forgetting something real fun too... almost put
The Toxic Avenger, but nah....
