If the zombie Apocolypse comes, the "Trusty" shotgun is being used only as a specialised weapon when available. for filling a hallway with pellets rather than barrier defense. Let the Other Survivors use a shotgun.
My primary firearm is very likely going to be the humble M9 Beretta. Against human targets, anything over nine millimeteres is overkill, and the ammunition for my actual preferred firearm (The Five-seveN) is just too rare to reliably scavenge.
Failing the practical use of the Beretta, my ideal backup weapon would be a halbred. It's got reach, a choppy end, and a stabby end is is pretty much designed for to kepe the slavering hordes away from me.
If quarters get a little bit closer than that (And the pistol would still be a poor choice), I may have to resort to a khetopesh or wakazashi. The former would be great, but the latter is easier to use, lighter, and more common.