Any of the three major calibers (9, 40, 45) are very good for self defense. Before buying a gun, I study and read many reviews. I want a good quality firearm, but mostly reliable. I do the same with self defense ammo. Yes many will say the gelatin ballistic tests are useless, but they are what the FBI use to test ammo. I want consistent expansion and most importantly not to over penetrate. I carry a 9mm and settled on Federal HST 147 grain ammo.