Most of the time they refer to themselves as Magic Mountain without Six Flags.
The park began as a completely independently owned and run park simply called "Magic Mountain" for nearly a decade before Six Flags ever bought it.
With the exception of Great Escape, I've been to every SF park in the states (so no Mexico or La Ronde yet, either). It's pretty subjective, because parks can have good days/bad days, good ops/bad ops. But overall:
1) Great Adventure. Simply because it's a great balance of coasters, flat rides, architecture, animals, theming, and history. Literally something for everyone, and has great re-visit value.
2) Magic Mountain. Even though it's my home park (aside from Universal), and the coaster line up is the best in the chain, and it (typically) has great operations (comparatively) and history. But it's significant lack of flat rides and only so-so theming pulls it down.
3) Discovery Kingdom. Not necessarily super notable rides, but again a very good balance of thrills, flats, and animals. Always something to do.
4) New England. Only got to visit this park for my first time this year, but really enjoyed it. Small, but friendly, nice atmosphere, and another good balance of theming and attractions.
5) Great America. So much to do and see! But the crowds can get pretty unruly, and the park is almost
too large for it's own good... getting around is worse than going around World Showcase lagoon at EPCOT.
6) Over Texas. Fun park, first in the chain. Not perfect, but many redeeming qualities. Shockwave is a great surprise every time.
7) Fiesta Texas. Unique location, some fun rides. That said, last time I visited this park was back in 2003, so my memory is a bit hazy and a lot has changed since then, so this went in a semi-random spot on my list. (Joker's Jinx was still around at the time, the backwards Arrow coaster.) Hoping to revisit this one again in a few years.
8) Over Georgia. Actually, I did enjoy this park, and it has some lovely areas. Nothing really "wrong" with it, although it can also attract unruly crowds at time. But nothing really "for" it, either.
9) St. Louis. I want to like this park, but it just feels disjointed, and the rides as a whole are not memorable (except the flat ride Excalibur, but it's basically as good as removed at this poiint, right?)
10) America. Again, this visit was many, many years ago (well over a decade), but I remember it looking dirty, unmaintained, rude crowds, and generally not a good experience. I'd be willing to give it another chance one day, but I'm not in much of a hurry to return.