When SHTF, I'd want to keep it simple.
Too many guns and other supportive stuff would probably have be abandoned.
If it's war, then one semi auto AR type in .308.
And one larger caliber high capacity pistol, something easy to find parts for.
If it was more survival, then a lever action rifle with a revolver in the same caliber.
Like .44 Mag.
No mags to lose.
And probably a pump 12 gauge, too.
Lock the doors, they're coming in the windows.