Actually, after seeing tests run by Rob Pincus and Phil Strader last year on Best Defense and again by Ed Head and Tom Gresham on Personal Defense TV earlier this year where the .223/5.56 round was shot through several constructions of combined sheet rock and insulation, which were placed about 15 feet apart from one another, I'm convinced that an AR 15, ideally with Hornady TAP rounds, is absolutely the way to go for home defense. This choice is closely followed by a shotgun with birdshot. Neither round will penetrate your home, unlike any handgun round available which will always exit your home if the proper backstop isn't used.
The high velocity of the AR .223/5.56 round, coupled with the yawing effect of the bullet, assures that upon impact the bullet fragments that may make it into a second segment of sheet rock are only tiny fragments that imbed themselves into the wall, unlike a handgun bullet which will just keep on penetrating right through the home and exterior siding.
It's really changed the way I think about home defense, especially with neighbors surrounding my home on all sides. Keep the AR by the bed with a magazine in a GunVault by the bedstand. That way the gun is still safe and unloaded yet readily available should the day ever come.