If I had to choose only one: OO-Buck for SHTF, because if it gets "that bad" and I have 00-Buck I "can get" bird shot, slugs, food, gold, and more bullets...
That being said, I keep my Mossberg-500 loaded with 00-Buck alternating with 1-oz. rifled slugs for 8 rnds. of incredible CQC destructive goodness.
Yeah dude I don't think the perps Momma would recognize em after you unloaded that barrage on em. GOOD LORD brother!