A lot of good comments from readers on this topic. There's a whole passel (that's Southern for a lot) of variables, some of which you can't know beforehand. For myself, I'd have to go with the 1st rule of a gunfight - have a gun. That means something that you'll actually carry as close to 100% of your waking hours as possible. Having said that, I'd still like a caliber that might get someone's attention, so I guess a workable trade-off is the .380. However, you can now get 9mm's that are just nearly as small and concealable as the smallest .380, and that's a big step up.
Just keep in mind there are no magic bullets, and don't expect one-shot stops. I enjoyed Clint Smith's comment that he only felt comfortable with the stopping power of a crew served weapon. A hit is always better than a miss, so take your time quick and get that first hit in, then work on fine-tuning your hits or evacuating the area at a high rate of speed.
jk