My favorite MB is probably TA from AFM. Its even more fun when trying to get the 1 Bil Hurry up when trying to start it.
One of the other MB's I liked to play most is from a game I really don't care for. Fellowship MB I think is really fun having to bash Balrog & then shoot a ramp to get someone over the bridge.
Seems Weapon X MB is widely considered a bad MB & I find it hard to disagree.