1 long gun for a survival type situation: AR type carbine, Riot Type Shotgun, or Battle rifle?

I would opt for a shotgun with an extended tube, something to hold between 7-9 shells. The mossberg 590 would be a good choice, but SKIP the folding stock. Its just one more thing to go wrong. The only addition i would do is combo or turkey style stock, with a regular stock and pistol grip.