Personally, I have a hard spot for the last level of The Islands. Got damn'd oni got me good with his realistic knife and unrealistic balls of pure flame.
After that, it's probably the Canyons minigame (that I think existed) where you had to get a bomb through a very tight and twisty cavern, like that section in Boom Town but worse. If that doesn't exist, mark down Boom Town in its place.
Third is that marshmellow level in Victoria's Laboratory. I think there's something wrong with me in relation to this one.