A nice little sub compact in a 9mm or better will do fine. The more powerful, the better. I prefer the 45, even though they typically have fewer rounds in the mag, because the encounter will almost always be decided by the first round or two.
I carry a Glock 26 at all times and my wife (TacDrivinMomma) ODT, carries an LC9 and she's probably a better shot than me. Just posing the question about the .22lr and appreciate everyone's perspective/experiences.