@Ryan, That might be true if you expect to move and fight nonstop! AR15 is still a goto for me as it is the more common rifle as far as parts to trade/obtain and ammo availability etc. I would keep it simple too. Non-piston, A2 upper or at least with detachable handle.

I imagine in SHTF scenario, it would be similiar situations in other countries when their govts fall. No food distribution, no water, no power, etc for some time. While you will have some anarchy, you'd be surprise on how many communities will band together for a common goal of survival.

Having saying that, I'd still prepare for the worst of course!