Well, let me do it this way .... I'll let you know what my 2 yo thought.
MGM - loved the Playhouse Disney show, Little Mermaid, Muppets, and Fantasmic (the part he was awake for)
Epcot - Loved the Nemo stuff at Living Seas, Imagination, and meeting characters
AK - Boneyard, characters, Lion King show (though a bit long for him) all hits.
We managed to squeeze MGM & Epcot into a day, leaving out some of the things Mommy & Daddy wanted to do. If you can pull that off, go for it. AK closes early, so keep that in mind.
Can't lose doing MK two days, though.