Somewhat of a vague question?
Should be answered in a somewhat precise way. Starting with what you need a pistol for?
Self defense is the most common reason, hunting Lions in Africa? Probably not a common answer, yes?
So if self Defense is the best bet, against humans would be the enemy/threat we are looking to defend against.
So, the caliber, and it's effectiveness against the human adversary, the living human body, is the first consideration.
The FBI have studied this for quite sometime, the modern Police carried calibers were dissected, over many years, basically the 9mm/.40 S&W/.45ACP.
First things first, how the projectile/bullet, performs in ballistic gelatin, looking at autopsy's, people who died from gunshot wounds, it soon became obvious, that there was not much difference, in the calibers, most important factor, bullet placement, what part of the anatomy was struck, and that the bullet could go deep enough to strike the organs, organs that are tied to survival.
But not pass entirely through the body.
We, the carriers, have now educated choices, based on massive dollars spent by the FBI, our only choice, is what we consider, the best pistol for us, our individual desire. Taking the FBI caliber selection as the main, common denominator, which was 9X19/9mm Luger to some.
As we have no idea how many rounds you need, for the threat you might encounter? Let us just say, more is better always! My choice the Glock 19 4th gen, which fully loaded, is a 16 round capacity, with a G17 spare magazine, more for the possibility of a malfunction, than the possibility of a 33 round gun fight, still no harm if it was a gun fight, that required more than 16 rounds!
Could it happen? It could, it has done so, not common, but it has happened.
Can you carry a Glock 19 concealed? I can.
What if it was one criminal, attacking you, and three rounds in to the central, upper body? Was required to get you out of this desperate threat?
Well, you have 13 left, not a problem.