Your question is best answered by testing:
1. How are you going to carry, and what gun meets that style of carry;
2. What is the largest caliber you can accurately shoot?
Being able to carry the gun in a way that is comfortable and usable for you will narrow down your choices of firearm, caliber and capacity. Second, you need to choose a caliber and gun size and style that you can shoot accurately every time (more bigger bullets don't make up for misses!).
Between the movies, guys like us talking smart, and the marketing of gun and ammo manufacturers, there is a lot of misunderstanding and confusion out there. A revolver full of .22lr put in the chest of a bad guy will make him change his mind quicker than a bunch of .45's flying all over ... except into the body.
Go to the range and rent guns, buy the ammo and try out your friends guns, and talk to people like you that have tried them. Then, let us know what you pick ... and post the porn
We love gun porn!