Disney and Universal are definitely the premiums (Disney, and I will argue this, is the highest tier), and offer truly innovative experiences.
Cedar Fair and Six Flags make amusement parks. Cedar Fair is slight notch above (I love what Ouimet is doing with Knott's), but still.
SeaWorld exists in the area between. They really, really want to duke it out with Disney and Universal but simply do not have the funds. Antarctica kinda nails it. They spend the most they can for an incredible, Disney-esque experience... only to find out that they couldn't purchase much more than the innovative tech Oceaneering offered them. The result was a (excuse the language) half-assed attraction that stupefies rather than amazes.