My son posed this very question to me the other day. We both agreed that Magic Kingdom was our favorite with Epcot and MGM running neck and neck. He still doesn't "get" Animal Kingdom--and is scared of Dinosaur!!! I think AK is beautiful--I love walking around and just looking at the trees and other vegetation.
Magic Kingdom is way above the rest for me, my whole family could just spend their whole vacation there My Sons would actualy like to just move into the castle, so they could be there everyday.
If I had to pick my second choice it woud be MGM...gotta love that "Tower of Terror"