I've probably mentioned this before, I work as a firefighter in a city where there is a lot of gun play. Shootings mostly are ambushes/drive-bys where 9mm and 7.62 x 39 are the primary choice. Clearly, if you get shot multiple times with either one of those rounds, you're screwed.

However, the most devastating one shot stops (dead) that I have seen were from .357 Magnum 125 grain JHP and 12 gauge 00 buckshot. Currently, the 45 ACP incapacitates like no other and the .40 S&W does well when placed well.

YMMV.