Modern semi-autos, like a Glock or HK are extremely reliable. (Forgive me if I left out your favorite brand

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The general rule of thumb in regards to recoil/caliber is this: Carry the biggest caliber that you can safely and comfortable handle. If you can put a good group up with a 9mm, but not .40 caliber, carry the 9mm. If the .38 is uncomfortable go with a .32.
Well placed shots are more important than big holes.....but big holes certainly don't hurt your cause unless they don't strike the target.
That's why a CCW permit to carry concealed is a must. By very nature, no one will know you are carrying. How would someone know they can take the gun and use it against you if they don't know you are carrying it? That's why open carrying is pretty much a bad idea unless you are big scary looking guy. Someone might see your gun and figure they want it more than you do.
So if it's concealed, and you are attacked. You now have the choice of what to do. You can hand over your wallet and purse, and never reach for your concealed gun and the attacker will be none the wiser. Or you can choose to stand your ground and pull the gun. Once you make the decision to use force you have to go all in. I teach it like when you are approaching a stop light that may soon turn yellow. You draw a mental line in your mind and if it turns yellow before that line you stop, if after you go through. Carrying concealed offers you the chance to decide where that line is.
Accuracy is a big issue if your shots hit bystanders. You may be forced to defend yourself in a mall parking lot or somewhere in a crowd. Even though you are perfectly justifiable in defending yourself you will still be held accountable for stray shots. Another case for practice, practice, practice. Use hollow point, deforming & expanding ammunition. These types of rounds carry a smaller chance of over penetration. They are safer for bystanders, and that means safer for you.