I guess it just really comes down to personal preference.
I have been to Disney World a couple of times, and it is almost perfect, but the wait for the rides is long and the thrill factor just isn't there. But there is so much they do right (shows, theme, food, etc). But, I also liked Disneyland better than World.....World I was ready to leave, Land I ran out of time...
Six Flags and Cedar Fair, if on a good day where there isn't many lines, are great fun. The rides are great thrills, but the theming isn't present or can be laughable. Food not so great, shows are okay, etc. Definitely a thrill seekers park.
To me SDC (and Dollywood) combines the two, plus throws in a natural wonder with Marvel Cave and the natural beauty of the trees and hills. The rides are fun, theming is present, food good, shows great, shopping, etc. - I just think SDC does a great job of having something for everyone.
So I could see how SDC and Dollywood are rated as a top 10 parks, however, I'm still baffled at SFMM being No. 1.
Jay
Edit......added the word Dollywood to try and make this fit that thread better.