I can personally think of two incidents where citizens killed an attacker with an AR15. I am sure there are more.
If I got into a shooting tonight, it would be with a rifle, because that is what is handiest at my residence.
If I KNEW that I was going to get in a fight with an intruder, I would put my pistol on my belt, and grab my rifle. Hell, if I hear a noise I go for the rifle first. I am primarily a pistol shooter, but the rifle is a more effective tool, and despite not being as comfortable with it, I shoot better with a rifle than with a pistol, and rifle rounds put more hurt on the bad guy than pistol rounds.