All kidding aside, it is really what the individual shoots best and feels the most confident with. Personally my choices are, in this order, .45, .40, .357 Mag and 9MM. The 9MM is a great round and will stop about any human with good shot placement. I like the size and weight of a .45 though. Any ammo testing I have seen shows that a 9MM might expand but a .45 will never shrink. In my short barrel, 3 inch, Kimber .45 I prefer to carry standard FMJ S&B 230 grain.