I would say Pirates, but once you’ve been to Pirates Disneyland, WDW version seems not nearly as good. For me it would be Tower of Terror. I like the creepy atmosphere, I just wish their was a little more to it.
One from each park: Magic Kingdom - splash mountain (pirates is a close 2nd) Epcot - mission space Animal Kingdom - everest MGM - Star Tours and Muppet Vision are a tie
Pirates, Space Mountain, Philharmagic, Mission: Space, MuppetVision, Imagination, Hollywood Tower Hotel, RnRC, Tough to be a Bug, Kali, Everest, Dinosaur...