Definitely MGM. If it weren't for ToT, I wouldn't bother. Oh, and DD15 had to go there for the HSM show. The new Monsters, Incorporated ride sounds interesting, though, and is it true they are going to update Star Tours? That would help. The Muppets show is getting a little long in the tooth as well.
Right now, IMO Universal Studios does the Hollywood thing far better than MGM. Lots of great attractions there - Revenge of the Mummy, Men in Black, Jimmy Neutron, Shrek, Jaws, ET, and the new Simpsons ride coming in '08.