If I had to pick one gun and only one gun it would be a 12 gauge Mossberg 500 or Remington 870.
Nothing beats a good shotgun in utility.
Just as an extra weapon (Zombie killer), we bought a Mossberg Maverick 12 ga. pump.(18.5 in. barrel) $180.00 at Academy Sports and Outdoors. It’s even assembled in the USA. Already have a Savage .22 rifle and a Baretta Neos .22 pistol