I can't think of any even remotely realistic scenarios where you'll be grabbing your plate carrier and rifle and heading out. It's fun to think about but it just isn't realistic.
Chances are if you do need to leave your house (or super duper hidden fortress you've bugged out to) you will want to blend in and not attract attention. Unless there is absolutely no police or military around anymore, I don't think you'll want to be running around town with any long gun at all. With that in mind, a handgun becomes important.
Your other consideration is, of course, defending your house / pillow fort / castle / sex dungeon. This can be done with the same handgun or whatever else you prefer, but you won't really be concerned with how much heavy ammo you can carry because you won't be carrying it.
Shotguns and. 22LR are great... if you live somewhere you can hunt, either right on your property or nearby. You won't be hunting much in the suburbs. Realistically, things are highly unlikely to break down to the point where we have to hunt to survive, unless you're in the deep woods and basically live of the land and don't want to deal with anyone at all.
Seriously, people, ISIS is not going to be paratrooping in Red Dawn style. The zombie apocalypse is not coming. Preparing for extremely unlikely scenarios instead of the ones that might actually happen is crazy, imo. Personally, I'm content with training with my pistol and shotgun. Eventually I'll get an AR but it's not high on my list of priorities right now, as I'm much more likely to need my handgun.