I chose a 40 s&w mostly because I can use 200 gr. hard cast bullets with a large flat meplat for woods carry around bears and do not shoot larger pistol cartridges as accurately. It’s the biggest one I shoot very well. A 9mm with the same hard cast bullets at 158 grains would probably work as well, but if I can shoot them similarly, heavier lead wins for my purposes. For carry in town, I shoot lighter fast hollow points for two legged goblins.