Least favorite Worlds:

Monstro (KH1)
Atlantica (KH1)
Neverland (KH1)
Pirates of the Caribbean (KHII)
The Lion King

I don't feel there has a been an entry I've played where I hated a majority of the worlds. Even clunky KH1 had more good than bad, though I do feel the overuse of some places, namely Agrabah, Hercules world, and even my beloved Halloween Town does make my eyes roll a bit. With that said, the game that actually has my least favorite set of worlds is probably KHIII, since only two of the new film worlds I actually liked, whereas I'm really lukewarm for most of the worlds. Granted, that might change once I play it because even though I don't like Toy Story, what I've seen of the world's design is actually pretty impressive an looks fun, so I may change my mind once I've played the world's much like BbS.