12 guage pump. Period.

Just racking a shell will deter 99/100 robbers right from the start. EVERYONE knows that sound and if you' re too stupid to immediately jump out the nearest window, well you deserve to be shot.

I' d load it with #2' s or BB' s so you' re not punching through the walls and hitting your neighbors like if you were shooting buckshot or a handgun. With a shotgun you don' t have to worry much about missing either.