Original Journey Into Imagination.
In addition to my previous statement about the original JII, I agree with Horizons as well. Many more guests (of all ages) got to enjoy Horizons over the current MS.I can't believe Horizons wasn't mentioned easier. Wouldn't be my choice but it's one people really seem to romanticize about.
In addition to what Danny suggested I still miss Food Rocks/Kitchen Cabaret and everything in the Wonders of Life Pavilion.