Gun for self-defense - making a choice

Do you meet the pre-requisities from my previous post and decided to purchase a gun? Then the next step is to choose the right one. It is a very important decision, because you are practically saying that you trust this specific gun with your life.
The first criteria is a caliber - you need something to make sure, that an attacker will be stopped after you shoot. In my opinion 9 mm at least. On the other hand you don't want the calibre too big, because then it increases the gun's size and weight - consider you also need to carry it concealed.... and possibly every day. You don't want a situation that you "sometimes" leave the gun at home, because it is not comfortable or does not fit under your current t-shirt. You would use such excuse more and more often and then it might happen the gun will not be with you when needed.
A magazine capacity - in most self-defense scenarios only 1-3 bullets are shot, so don't worry about this one much.
Reliability - a very important one, spend time reading about other's experience with a specific gun model, regularly train in a shooting range.