Painball is just really cool overall. It has the charm to it (after all, this isn't the first time in the series Bowser used a pinball table) and it feels pretty fair, although personally I would prefer the "painballs" did -2 hearts with each hit instead.
Roulette Rage is also good. It doesn't feel like it's unfair at all, though I can tell depending on the players' reflexes, it can be very one-sided for Bowser or the team.