I carry and own all three major service caliber, those being the 9mm the .40S&W and the .45acp. I like the 9mm as it's cheaper to shoot and easier to shoot and carries the most rounds in a given handgun. I know handguns are a compromise anyway, so I carry a 9mm most days because I can shoot it the best whether two handed, weak handed or one handed, it doesnt matter.
My buddies who served in Iraq both shot men with their M9 pistols with FMJ ammo. No HP ammo, just FMJ and both men went down and stopped what they were doing and never moved again. Shot placement is everything.