Its hard for me to say for a variety of reasons:
- It would have been Mr. Toad's Wild Ride, but I got the chance to ride it when I went to Disneyland in 2011. So I didn't feel like I was missing out anymore. Same explanation with 20,000 League Under the Sea and the Nemo Subs (yes I know the experience isn't the same, but it is similar enough).
- I never had the chance to experience Horizons, it was closed when I was 5 and I obviously cannot remember if I rode it or not when I was 2.
- I was 5 the last time I rode World of Motion and Journey into Imagination, so while I remember them, they don't have the same sentimental feeling if say they would have still been around when I went when was 11. Also I understand why both of them had to go, even though the execution of a new Imagination could have been much much better.
- The new version of Spaceship Earth does not bother me. Seems like a logical update and in a way incorporates some of the spirit of Horizons. I do agree that the decent could have been done better.
- Never went on Alien Encounter, would not have gone over well, haha!
Finally to my choice:
Wonders of Life pavilion was probably my favorite "extinct" thing at Walt Disney World. Loved Cranium Command and I thought Body Wars was more intense than Star Tours, which always made it more trilling for me. Plus the other stuff around the pavilion was always fun and I loved that everything was connected to a common theme, which we really only now in The Land.
Maelstrom will take over the top spot if the rumored Frozen takeover does indeed happen.