Logic would tell me that you carry the biggest calibre that you can easily conceal, feel comfortable with carrying, and can actually shoot with accuracy. Personally, I know that regardless of those on the forum who find everyday life to be a small step away from murder and mayhem and must CC literally 24/7 with some form of bazooka, I am uncomfortable with anything on me other than my clothes, a credit card, a $20, and a car key; when I decided to minimally carry (in car for road rage, at night) it had to be small and very light or I would not bother. KelTec P3AT (380) does the trick. ,