I have to go with the old model Ruger Vaquero in .45LC. It's beefy and simple to operate, works well with cast lead and black powder ammunition, just like the old days.
Guns may actually be fairly plentiful after SHTF, but ammunition won't. Learn how to make your own black powder and cast your own bullets.
If you really wan't to survive, learn how to make black powder, get yourself a good flintlock with a big bag of flints, and a bullet mold.
Flintlock rifle for food, Ruger Vaquero for protection, and maybe a little .22 revolver and a few bricks of ammo for whatever.