First, I think Stitch belongs to Magic Kingdom because this park is the most representative for Disney animated movies. Yes, I know that MGM is a MOVIE studio, but where is Cinderela's Castle? And where is Peter Pan, and Snowhite, and Buzz Lightyear, and Cptn. Hook, and Iago and Zazu? I don't know, Magic Kingdom IS the Park for Disney animated magic.
That being said, the Stitch ride storyline takes place before 626 lands on Hawaii. If you remember the movie before credits, is very modern and futuristic, with aliens and ships and robots. And if the timeline is BEFORE Hawaii, Tomorrowland is perfect!
Someone said Stitch could go on the Tiki Room. No please! That show was ruined enough, we don't need anoter "great and creative refurbishment" of the kind that "Journey Into Imagination" suffered.
That's my opinion on the matter. And other thing: "Lilo and Stitch" is considered to be the best traditional animation movie since Tarzan, so, it very well deserved to be on a ride or show or something.