Almost any of the sub-50-grain bullets will work pretty well for certain purposes. It just depends on what you want to do with 'em. If you want 'em to tear things up at lower velocities, instead of just punch a nice hole, plastic-tipped bullets tend to expand most reliably.
By the way, Midway has 40-grain Varmaggedons available now, but they're the hollow-point instead of plastic-tipped version. The HP's don't expand as violently, but they work pretty well, and are very accurate.
