9mm or 40 s&w are OK, just don't get a diminutive gun, they are marginal.
And remember guys, the s&w was designed for FBI use, and look at the flat nose is designed to stop and drop a subject.
Also make sure the barrel is no less than 3", for efficiency, short arms like revolvers, use longer shells to make up for the short barrel.
A small keltec pf9 for personal protection is good, and Don Davis, I think berettas are the most beautiful pistols, but they are not too small for real concealment, if they were cars they would be jaguars.
Here a Keltec PF9 with night sights from glow-on.com, nothing fancy nid you, but in a hurry, it can save your life.