Some folks think that a low recoil 9 pellet 00-buck is good. Others want slugs. Others want some #1 bird shot. Some folks want a mix of shells in the magazine / side car.
I'm personally a fan of some 3" magnum 12-15 pellet 00buck-ish. Kicks like a mule, though. Make sure to practice with this heavy of a load on occasion so that you're semi-used to how it behaves.
I don't subscribe to multiple shell types in the magazine. That requires extra thought during bad situation, no thanks.