Buy what fits your hand and that you can shoot well. Any round is a good choice provided you are capable of doing what is needed under pressure. Six quick shots from a 22LR. with CCI solid stingers in a 3" group will stop anyone in thier tracks.
Practice,practice, practice is the key. Buy a GOOD HOLSTER and a BELT DESIGNED FOR A HOLSTER. The hardest thing to conceal on any handgun is the grip. A well designed holster and good belt you can carry a Govt Model 1911 or any other auto or revolver. People who complain about a firearm's weight or size 9 times out of10 have skimped on the holster and belt or went for a decent holster and skimped on the belt. The Uncle M's nylon and such holsters don't cut it and neither does a normal dress or sport belt.