Hanenbow, the stage no one remembers about.
I'll take it over WarioWare any time.
Honestly, I'd gladly remove WarioWare, 75m, Mario Bros., and Hanenbow from the game. Pictochat is fightable enough that I'd keep it in. The rest can leave forever. I'd normally say New Pork City too, but it has a lot of decent areas to fight on and isn't nearly as terrible as the first four. Plus, it's probably coming back anyway.
Mind you, the only DK courses I like is the first game's and Jungle Japes. Mario's are mostly good, but I don't like Mushroomy Kingdom(either version) or Mario Bros. Wario has no favorable courses for me. I wouldn't mind WarioWare as much if it couldn't easily kill you and it made people temporarily invincible, making it beyond horrid for Single Player. It's just cheap Fake Difficulty that shouldn't exist. It has no fun in it outside of casual. As a person who mostly plays competitively, and wants to actually win the Single Player modes as is, these types of courses shouldn't exist or be an option in that mode. Oddly enough, Halberd and Port Town Aero Drive are really safe compared to the past courses. Lylat Cruise is the same compared to Corneria(who can't much kill you either, and it theoretically more easy to fight on).
To note, I think All-Star and Classic should've let you play on any course for the character possible that's among their franchise(via its symbol). I think that would've been nice.