Super--while you're busy playing with your noisemaker trying to scare him off, a serious opponent will be busy noting your position and armament, if not putting a few rounds through the wall at you.

You're in a fight for your life. Don't give away any information or advantage.

Tell you the truth, I'm somewhat puzzled as to the permanent affinity for the shotgun. It's not aim-free, it can be short-stroked, it's bulky, the capacity is extremely limited, and it's very slow to reload.

Personally, I feel that the "best" option starts with whatever firearm the likely user is most familiar with. Maybe it's a shotgun of some sort, but a full-size pistol, large-frame revolver (a 629 loaded with .44 Specials, for instance), or pistol-caliber carbine would do just fine. I'd probably discount leverguns and single-action revolvers, though.