AR 15/10 would not be on my strictly home defense top 5 list. The best home defense weapon is a cylinder bore shotgun that holds multiple rounds of high brass 4 shot.
Rationale: True home defense is close range, within your house. Absolute max range of 60 ft. Shoot someone outside your house from inside and you won't have to worry about a house cause you are going to loose yours when the perps family sues you. Bird shot is not lethal after going through 1" of Sheetrock, therefore your family and neighbors don't catch stray bullets. And in a dark, high stress environment you can still hit your target without being ultra accurate. Even if the perp is carrying his own weapons, after taking 1 1/2 oz of 4 shot to the face at 25 ft, he won't be as interested in harming you.
As for any AR right now, they are not as cheap as they were just a couple months ago. A build would be the cheapest option. And it's fun putting it together.