I would say Dinosaur only because it hasn't been talked about or acknowledged in a long, long time. Some people I've met didn't even know Disney made Dinosaur and argued it was another studio that did, very vehemently.
All are agreed. I'll add Song of the South. Yes, Splash Mountain contains characters from the film. However, there isn't a child today that would know what movie the characters came from. Some of the best songs in Disney history in this film.
That rides been there, as Countdown to Extinction, they just overlayed it with DINOSAUR because of the release of the movie, besides the ride, I don't see any other stuff out there relating to DINOSAUR, like a sequel..