Boredom is the worst hazard, so no FD for me.
Nah, kidding. But Spirit Train looks annoying (Like Big Blue but instead of being from my favorite racing game, from my most-disliked spinoff of Zelda), not gonna be a big fan of the Nintendog stage in any way, and the Golden Plains may be a tad too silly to play on with any frequency. No qualms with Devil, Brinstar's acid, or space pterodactyls (playable or unplayable).
Not really looking forward to fighting Wakamoto on Gaur, though, if that's unavoidable.
Edit: I somehow forgot Mushroomy Kingdom. It's a cool idea, but I do not intend to ever select that stage voluntarily.