Short barrel 12-gauge pump style shot gun. Standard dove loads are best. Plenty of stopping power and not as likely to penetrate the outside wall of you house and risk your neighbors.
You will get lots of differing opinions on handguns. The most reliable are old school revolvers (some semi-autos jam with some kinds of ammo) . Medium length barrel 357 magnums are one of the best one-shot stoppers.
I like my Taurus PT92AF 9MM (Beretta clone). Thousands of rounds of various kinds of ammo and its never jammed. This handgun with Corbon +p+ 115 grain loads is a proven combo. Other good choices are the 40MM, 45ACP. The advantages of a semi auto over a revolver are more round capacity, less recoil, and easier reloading (additional clips).