Forget any automatic. Unless you are trained, practice often and maintain the weapon in meticulous fashion you will run the risk of jamming or stove piping after the first round. If you are willing to seek the right training and maintain you skills then there are a number of autos that will work. The best hand gun ever is the m1911 .45 acp. Almost a century of smooth, accurate knock-down power. But, I would hesitate to use this power in a home environment, especially with others in the house. Although I own a variety of personal defense weapons the one I keep at hand in the house is a S&W model 40 2in revolver. I use a Federal 138g load with pre-fragmented hp. The low load provides knock down power, the bullet mushrooms then breaks up so there is no through and through. These pistols will fire time after time with little or no maintenance. If you need more than 5 or six shots then you've already lost.
As for shotguns, try turning the corner at the bottom of the stairs, at 3:00 a.m., when you are scared and inexperienced. In situations like that close quarter target acquisition becomes a nightmare.
No matter what you decide to do, make sure you get the proper training. Good luck.
Good post! About time someone put the shotgun as your primary home defense weapon in proper perspective