The one advantage of the AR platform would be the ability to have an upper in 450bushmaster or similar, or a 243/25 WSSM for hunting, then an upper for defensive purposes in whatever floats your boat. There was a 30 caliber variant of the 5.56x45mm IIRC as well. An AR10 platform would perform better for hunting, but like what was said, urban home defense would not be ideal with one. For the cost of the platform, there are plenty of inexpensive bolt action rifles available in calibers easier to find right now.