Well one thing worth noting about Super Monkey ball is that it was a release title. It is dissapointing for a couple reasons, but considering its only 30$ retail now, its worth the money if you've got friends to play with. However as a one-player game, it will get boring fast.
Zach and Wiki I have not played, but I have heard nothing but good things. But thats not a multiplayer game like monkey ball.
I think you should ask yourself, are your friends around enough to make monkey ball worth it, or do you play more often by yourself, in which zach n wiki would be a better choice.