I have a difficult time picking favorites, because I love rides but....
Peter Pan's Flight - you've gotta love a ride that makes you feel like your flying. Even now that I'm older and I can SEE the track... I still love it. I even got stuck on it the last time I went, and thoroughly enjoyed staring down at London for a few minutes.
Buzz Lightyear's Space Ranger Spin - My whole family LOVES this ride. We go on it multiple times every trip. It's extra fun, because you get to experience a little bit of competition.
Soarin' - Once again the flying thing, and the smells. I have this thing for things that smell like oranges. When I was little there was another ride at Disney that gave me the orange smell, but I don't remember what it was and I think it must have closed (I haven't come across it sense)... It involved pushing buttons. I might be wrong, because I also remembered candies from somewhere in EPCOT and my whole family was convinced I made it up, but I recently figured out what they were on here. You get them in Japan and they have edible wrappers.
In Disney Studios/MGM I have a more difficult time picking a favorite, because I love everything. Probably ToT. It is an excellently themed ride.
Animal Kingdom I love for the atmosphere. Everest is awesome and so is the Kali River Rapids. I love Kilimanjaro Safaris too.