My choice would be to keep a pump action 12-gauge shotgun, one of my Mossberg-500s.
First off, the variety of loads available for the 12-gauge shotgun provides the means to bag game ranging in sizes from mallards to moose. Birdshot, buckshot, slugs, and sabots, are all available and affordable.
Second, the reason that law-enforcement and the military use 12-gauge pump shotguns is because they are reliable and effective.
The Mossberg-500 is versatile, having interchangeable barrels available for any hunting or home-defense contingency. If I desired, for home defense I could remove the shoulder stock and put a pistol grip on the gun.
I consider a handgun a better primary home defense weapon, but if I can only have one gun, a shotgun will be it.
James A. Zachary Jr.