There are 3 probable guns to have, a pistol, a shot gun and a rifle. Looking at the theoretical EOTWAWKI with a zombie pestilence I would look at it differently. I would have a hi cap 9mm, a 12 gauge pump and a .22 rifle. That is assuming I have a vehicle to carry them and me. If not then I am going for a smaller .22 rifle by itself and a brick of ammo with the pistol and a couple extra mags. The 22 is easy to shoot, not as loud as the shotgun or pistol and plenty accurate for melon busting at 100 yards. In the case of the zombies, being unseen and unfound is the better option.
Now if you are assuming the fast running zombies, kinda hard to accept given they are zombies after all, then the 12 gauge is better.