Well, Six Flags Great America did not start out as a Six Flags thing. I mean, it was owned by Mariott, and that is why it's so much better. It got a better start than other parks owned by Premier or Six Flags... although Great Adventure was a Mariott park too....
GAM got American Eagle, Demon (and the former) Rolling Thunder, Tidal Wave, and the Edge, a bunch of rides I really liked compared to some Arrow clones that Six Flags put in the park (not to mention aaaccchhhhShockwavechhooo! any names.)