My experience is that 45ACP, while a century of empiric evidence espouses it a capable anti-personnel round(JMB himself designed it as such, and built the 1911 around it, as a delivery system for the round) it has lousy penetration characteristics, just short of anemic. .44 Mag, quite the opposite, but bear in mind you are using 3 or 4 times the powder load on approximately the same projectile.
9mm has excellent penetration characteristics, by comparison to 45ACP, using about 65 to 80% as much powder to drive a bullet about half the weight and cross section. The greatest benefit of 9mm is it's overall recognition and acceptance as an efficient round, and all the fine pistols which have been chambered in the caliber. The higher capacity of 9mm mags, IMO, gives a superb advantage to the caliber, as well as it's accuracy enhancing lower recoil.
But it's still a buck-dancer's choice, as to which to use, for personal defense.
9mm has excellent penetration characteristics, by comparison to 45ACP, using about 65 to 80% as much powder to drive a bullet about half the weight and cross section. The greatest benefit of 9mm is it's overall recognition and acceptance as an efficient round, and all the fine pistols which have been chambered in the caliber. The higher capacity of 9mm mags, IMO, gives a superb advantage to the caliber, as well as it's accuracy enhancing lower recoil.
But it's still a buck-dancer's choice, as to which to use, for personal defense.