I'd have to go with Luigi's Mansion. The layout of GHZ is kind of awkward with a big dip in the center. No one likes getting thrown off the edge. And what is up with those stupid check points. Someone always has to attack them first just to annoy you. The music is okay, but if you ask me, a lot of the sonic music is annoying (at least the ones with words).
Luigi's Mansion has interesting music (Tetris: Type B?), two flat platforms, and no real match interupters. Plus, it has DESTRUCTIBLE PLATFORMS!!! I mean, who doesn't like that? Sure you'll say, but so does GHZ. Yes, but the ground just falls and blinks back to the original spot. The Mansion floats up and reassembles itself which is a little creepy.
IMO: Luigi's Mansion>Green Hill Zone