Following the link in my sig will take you to a direct explanation from a legitimate, legendary expert on terminal ballistics in humans on what works.
Dr. Gary Roberts has seen more bullet wounds and knows more about shooting deaths than almost anyone on this planet.
His advice: all the standard service calibers (9mm, .40, .45acp) work as well as you can reasonably expect a pistol round to work.
The advantage of the heavier rounds is not that they perform better on humans, particularly - there is in fact very little difference. It's that they handle intermediate barriers better.
On the other hand, 9mm and other fast, light cartridges tend to do better on soft armour.
Rifles and shotguns loaded with buckshot work better than pistols.
Nothing works if the person is not hit in a vital organ.
Shot placement is everything. Caliber is a small factor and not worth worrying much about if you're defending yourself against another person.