I personally think that Skippy wins, even though Squash Monster hasn't fully realized his potential. He's forgetting several extremely useful forms, such as Will-o-Wisp, that gives extraordinary flight and invisibility (greater, I think? It more of a suppresses the light than turns invisible).
And if you want to get your hypotethical DM kill you, get Frozen Wildshape and turn into a 12-headed cryohydra that casts as a 20th level wizard.
This whole build is versatility embodied, I think. It could be thought that that's just becouse I'm a fan of MoMF.