It was said: "A shotgun is the absolute best HD weapon for virtually everyone."
Please remember that statement is an opinion, . . . nothing more.
A shotgun can easily become a liability when the BG has hold of the barrel, . . . when all 3 rounds are shot out of it, . . . when you cannot get to it because it is in the other room (vs pistol on the belt or in the pocket), . . . or when it gets its barrel stuck coming around a corner in the hallway, the curtains, or a myraid of other places and things.
A shotgun has it's place, . . . but as an HD weapon, . . . it is just a choice, and for some is great, . . . for other's it is more of a liability.
A shotgun also requires much more training to become operationally competent with it, . . . than does a pistol or a revolver.
May God bless,
Dwight