I think I would agree that a magazine fed, breech loading shotgun is the most versatile firearm. However, firearms in general, should rate surprisingly low on the list of survival necessities, well below the significant needs of water and shelter, fire,etc.

In my own survival or near survival experiences, plus the times when I helped others in such a situation, I can not recall any time when firearms would have been particularly necessary or even helpful.

Firearms seem to show up mostly in the fevered fantasies of Mad Max, shtf, wrol, etc scenarios which don't usually even come close to reality.

I do a nice assortment of firearms because they do come in handy from time to time, and frankly, they are enjoyable. If it came down to it, probably the most potentially useful would be my AR-7(takedown 22) or my good old Mossberg 500 shotgun. In the long run, neither would be as helpful and a good climbing rope.