It's really hard to pick just one favorite ride, since there are so many different reasons for loving different rides. It's hard to put one in front of the other.
If forced to pick just one, I would have to go with TTA. It's a relaxing, very enjoyable ride where you can kick back and rest your legs after a long day of walking around the park. It's covered in shade, which is great, especially on really hot days. And, growing up, I always loved being able to go inside Space Mountain. I always thought that was the coolest thing.
And just so I don't feel bad for those rides that came close, but didn't quite make it, I'm gonna round out the top 5: Splash Mountain, Jungle Cruise, Great Movie Ride, Rock & Rollercoaster.
My favorite "extinct" ride would definately be Mr. Toad's Wild Ride. I don't know what it was about this ride that made it so special for me, but it was always the ride I looked forward to going on the most. What I wouldn't give to ride it... just... one more time.