I find it amazing that people consider using a rifle for home defense. Why not a trusty shot gun? They are far cheaper than a AR and less aiming when in low light
An AR-15 is a far superior home-defense weapon than a shotgun in my opinion. A shotgun's recoil can be difficult for some people, especially smaller, newer shooters, whereas the AR-15 has barely more recoil than a .22. Also, most AR-15s are shorter than most shotguns and much easier to use one-handed. Pump shotguns can be cumbersome and require two hands, and semi-autos aren't nearly as reliable as an AR-15; and unless the shooter is extremely consistant, even a pump is less reliable than an AR. And I can put 2 or 3 rounds center mass as fast as I can hit just once with a shotgun, making the AR far more devastating in the same amount of time. And contrary to popular belief, you do need to aim with a shotgun; at home defense ranges the blast is only going to spread a few inches. Also, an AR is going to have a much higher magazine capacity and will be much faster to reload. In addition, light plastic-tipped .223 varmint rounds will punch through soft body armor but will penetrate far less through walls than buckshot, meaning you're less likely to kill your neighbors or family members in another room.
There's nothing wrong with using a shotgun for home defense, but I think an AR-15 is easier to use, more effective (especially against multiple attackers and people wearing body armor), and also safer for innocent bystanders because of less penetration through walls. The only real disadvantage is cost.