In a SHTF scenario, if I had to travel with a gun larger than a pistol, I guess the key question is will I have to carry this gun outside of a vehicle at times?
If so, I want the ability to CONCEAL it. Be the gray man, not the open-carry guy attracting attention, maybe pizzing people off, especially if you're a stranger to their area (just passing thru).
Also, there may be military / police out there detaining people for open carry, or disarming visibly armed people.
So unless you're in an all-out war, shooting bad guys and cops and national guardsmen all alike,
I say there's value in sometimes tucking an arm-braced AR "pistol" under a coat or inside a folded blanket or in a duffle bag, esp. in urban / suburban areas.
In that scenario I'd want either 300bo or a b&t apc10. I assumed "shtf" and "which long gun" did away with concealment scenarios. Probably the 300bo with a quick detach suppressor and a variety of rounds.