Ahhh yes. The game where "Luigi Blew It" came from! 
Now I need to know what this inside joke is about. It has something to do with singing along to the underground song, right?
Actually, I think Toad was the best myself. His superior fast pulling ability made him so very very good against enemies and bosses.
Not to mention he can snag you a few more coins if you enjoy the bonus game.
...shortly after I got out of the Negative World, I quickly picked up a small turnip as Toad. Next thing I know, it's stuck on his head, and any items I pick up still work, but I can't see 'em!
Once you go through a door (or maybe even a ladder, I haven't checked) to a new screen, the object that got stuck to your head becomes throwable again. This can be abused to place Subspace doors where they weren't intended to be, among other things!