I know it isn't exciting to most people, but my favorite ride is, without a doubt, the WEDWay PeopleMover (now the Tomorrowland Transit Authority). I'm not a rollercoaster fan, so the mountains don't really appeal to me, and while there are some other fantastic rides (HM, Small World, etc.), the PeopleMover, by far, is my all time favorite.
For EPCOT, not entirely sure. Journey, though it is now gone, was probably my favorite. Horizons, also gone, was up there as well.
MGM, I used to like the Backlot Tour, but it is apparently a lot shorter now, so I'll go with Star Tours (I know it's the same principle as Body Wars, but I am grossed out rather easily).
The Monorail is great. I like it alot though it isn't technically a "ride."