I got this question recently from someone who felt less than confident carrying a five shot Taurus 85 revolver. This was my reply.

I prefer six, because if you have three predators, that gives you two shots per predator. But, unless you want to pay a lot of money for a Kimber or Colt, that is out of the question. I like the 85 and for summer time I mostly pocket carry a 605 which is identical, but two ounces heavier, and chambers .357. The 85 handles +P fine, so I would look for a 125 grain +P you feel confident with. The Remington copper jacketed hollow point is one I started carrying recently.

I do not endorse this shooting in anyway whatsoever, but do some research on the Bernard Goetz case in New York as far as using a five shot snubbie against numbers. The tactics were good, but the use of force was more than what was warranted and once a perceived threat is over, you don't shoot someone retreating or down.

Other than that, consider a single stack semi-auto like the new Ruger, which is very reasonably priced, the M&P Shield, or the Taurus G2 which is an extremely popular gun. I've watched professional trainers go on and on about capacity on video using the absolute worst case scenarios for law enforcement as examples (subliminal message - live in fear and buy my training).

For most people, a five or six shot revolver or a single stack semi-auto will be more than enough to get you out of the types of predatory situations most common. If you go rough places or live in a rough area, carry more, but the main thing is, carry what you feel confident in and train with the gun you will be carrying.