I had to go with Dumbo. It's a must ride every visit. When someone tells me their going to Disney it's the first image I think of. Now if you would've asked about CA then I would've said Screamin'.
My favorite is actually at DCA (TSMM) but for DL its a close one ... Space Mountain was my first choice but there are several that are very very close. Star Tours wasn't listed but made my personal top 5
Pirates...because...it's Pirates! We make it our last ride every visit (used to be Small World when the kids were little). Last July we went for our last ride, it was late, and we had the whole boat to ourselves...just the 5 of us. It was a lovely, memorable family time for us.
Peter Pan's flight is my favourite dark ride (though Indy comes close), and Splash mountain is my favourite coaster-slash-dark-ride. Space mountain comes a close second though, without the noisy Halloween overlay!