Voicing my personal opinion here, so here goes. Hands down, the .45ACP is the proven choice.
The 9mm is a good cartridge and had served the adversary's military well in WWII and beyond, but stopping power is dependant on shot placement. Same for the 10 and the 40...pretty powerful and deadly, but... There's a reason why most combat pilots and grunts buy their own .45's instead of carrying their issued hand weapon. Add to this Corbon or alike ammunition and the informed argument ends,
They all kill, quite well. But the car analogy might apply here...what would rather send a threat their way, a sports car or a freight train. Both will do the job, but the freight train guarantees an end to the threat regardless of where it's hit.