you need to consider what your house design is and neighbors. while an ar is an excellent weapon it will go thru a couple houses if you miss. also you dont want to be sticking a long barrel around corners as its a dead giveaway your coming and an awesome lever for someone to grab on to in an effort to disarm you. ofcourse training and common sense mitigates these issues.
i personally think a shot gun or hand gun are the best choices. its a toss up between the two. one is more precise the other more forgiving.
the best is a 12 inch shotgun. sure you need to get an aow stamp but its powerful forgiving and can be maneuvered around easily.