I've got a Colt 1911 and a Mossberg 590A1 12ga 20" bbl. Which one I pick should the need arise is going to be an on the fly judgment call, if I believe I have time (they are in the process of kicking my door/window in) it'll be the shotgun, if not (they have already breached
my perimeter) it'll be the 1911.
What I'm getting at is you can't have too many options, I'd pick up a 18" barrel 12ga pump and a pistol if funds allow.
As for pistols, use what's comfortable to you and shoots well in your hands, go pick a few up at a gun shop and buy the one that just feels like it belongs right there in your hand. For me that's a 1911, for you it may be a Glock or a Smith and Wesson revolver or who knows.
If I were to throw out requirements it would be this:
Caliber- Revolver: .38 Spl or .357 Mag
Semi: 9mm, .40SW, .45 ACP
(all are common and considered effective antipersonnel rounds and cheaper than other choices such as .44 Mag, 10mm auto, or .357 Sig)
Size- 4" bbl or more (no sense in going smaller since it doesn't need to be concealed)
Sights- I would prefer night sights but you'll pay extra
I am absolutely NOT an expert, these are just my personal preferences so if I left out someone's favorite caliber don't hate me, last time I checked it's still a free country and you can love the .380 ACP, .32 ACP, .22lr, .50AE, .50 BMG
... whatever all you want for HD, these are just what I would choose.