I thought about this for a long time before I started really carrying concealed everywhere. If you carry concealed, that means "whatever" situation is probably going to be close quarters. I chose the NAA .22 Magnum 5 shot revolver. I carry it in a legal, leather pocket holster, with five more rounds in a snap pocket in the holster.
Inexperienced people always laugh when I tell them I carry a .22. All of my close law enforcement friends, and I have several, all agree they'd probably rather take a .38 shot than a .22 Magnum. It's a nasty little round, especially the little hollow points I carry in it. It's light, small and I've had to tell myself, "Rob, go put that back in the car", because I even forgot it was there, when we'd go in for like a car tag or somethin.
lol
It's only a 1 5/8 barrel, but if you practice with it, you can bust a bullseye at 25 yards with a hip shot. I can.