Depends what you mean by "best". Splash Mountain is a very good ride. Peter Pan's Flight is ridiculously popular. And the non-movie rides, like Matterhorn and Mansion, were created in-house by the Imagineers. So they're still authentic Disney, whether they tie into a movie or not. None of the great ones were based on non-studio-generated IPs that were purchased and then shoehorned into the parks. Even the Twilight Zone Tower of Terror, based on a non-Disney TV show, was originally conceived as merely a haunted Hollywood Hotel whose ride narration was originally going to be provided by Mel Brooks (odd choice, if you ask me, unless the Tower was originally supposed to have a macabre sense of humor, like the Mansion). What I'm saying is, visitors to a Disney park prefer the park to have a Disney flavor - and Marvel doesn't have that flavor. And it never will.