For home defense (inside the home) an AR-15 is quite possibly the worst choice. The bullet travels way too fast, and way too far to make it effective indoors.
Even hollow point .223/5.56 ammo is travelling way too fast to open properly at close range (less than 25 yds). More than likely it'll just go thru the bad guy, and thru a couple of walls before finally stopping. If you are shooting in your home you must ALWAYS be certain of the background, and where the bullet is going to go once you pull the trigger. You certainly don't want to accidently shoot a family member because they're too close or on the other side of the wall downrange.
If anybody doubts these statements just go to youtube and look up AR15 wall penetration. The videos will let you see just how the bullets will react to walls and other objects.
In the gun shop I work in we generally tell anybody choosing an AR-15 for home defense to make sure they tell the neighbor that they intend to use the AR for defense. That way, if the neighbors hear gun shots, they'll know to get down into a basement so they're not accidently shot.
A short barreled shotgun or a handgun strategically placed in the home are generally better choices for home defense. And even with those choices, you must always be aware of where the bullet will go if you miss, or fully penetrate the bad guy.
Lastly, shooting somebody in "defense of property" is not just a bad idea, it's also illegal in most states. There is no personal property on this earth worth taking a persons life over.