I can't pick just one ride overall! They're too good! But I can pick one from each park.
Animal Kingdom: Dinosaur because for years I was terrified of going on it. Then, once I finally did, I was hooked. I've always been a bit of a science nerd so, of course, I love a ride that's Dinosaur and archeology themed!
Epcot: Soarin', most definitely. I love it because it is just so wonderfully done that you really feel like you're soaring over California--it's such a relaxing but entertaining ride.
Hollywood Studios: Rockin' Rollercoaster, hands down. I love a good adrenaline rush.
Magic Kingdom: Splash Mountain. I love the theme, the music, the views of the park, the drops--oddly enough, I absolutely hate the final drop but I love everything else about it.