One shot should do the job.
I would never question that a 12 gage does the job nicely.
I just question if it is the best tool for home defense for the average home owner.
My personal choice is a Colt 1911 with Cor-bon safety slugs.
Hits hard and doesnt penetrate walls.
I can point and shoot out to 20 yards and hit a man sized target. Its all I need.