I did love Mr. Toad, Captain EO was cool, and the Skyway was pretty, relaxing, and convenient. BUT my vote is for HORIZONS!
I remember when I was little Horizons was my absolute FAVORITE ride! I would make my parents ride it over and over, and I would get to pick a different ending each time (but I liked Land the best!).
The first time I was there and it was gone was my only disappointing experience at WDW.
I still miss it!
P.S. I can't believe Alien Encounter is gone! That still seems new to me. I only got to ride it a couple times, and it was truly terrorizing!