I would agree that the Plaza has a wonderful burger (along with everything else). Also Beaches and Cream is up there too. (You notice no one is offering CS, only TS??)
Another vote for Sci-Fi! We have eaten both there and Beaches & Cream several times. Sci-Fi burgers are bigger and better but correspondingly more expensive. B&C burgers are good and an excellent value.
Ironically I once heard a CM at MGM claim that Sci-Fi burgers were "the best in the park"! Better than Backlot Express and ABC Commissary? For $12, I certainly hope so! I think one could make a bolder claim.
I've never eaten at ESPN Club, a stone's throw from Beaches & Cream. How do they compare?
I have an odd nomination: Restaurantosaurus. Not for the McDonald's burgers, but for the Disney-brand veggie burger sold here. (and not sold anywhere else that I can find). Compellingly tasty. And no guilt