Caliber debates about pistols are worthless

[Jer]

People ask me regularly what they should carry and why. My reply often is whichever gun they can hammer fire through a mag the fastest and maintain the smallest group. You can train all you want and envision every possible scenario your mind can think of and the reality is that when your life is actually on the line and you get that adrenaline dump that's exactly what you're going to be doing no matter how cool of a cucumber you think you are. Now, if by some miracle you're able to slow down and take your time then that's wonderful and you're not out anything. Plan for the worst and hope for the best.

This invariably is 9mm over 40 & 45 for most. You also get higher capacity (more chances at that perfect shot in the same size frame) and another consideration is the cost & availability of ammo.

With advancements in ammo technology the playing field has been leveled. Keep in mind that handgun calibers just poke small holes so I want to poke more holes and have more opportunities to poke holes in the right things to stop the threat.

The idea that .45acp is a better defense round than 9mm has never been more false than it is today.

Train with what you carry and be proficient with whatever it is. Then be aware of your surroundings and avoid potential bad situations as this is these most important things you can do regardless of what caliber you choose.

Edit: I forgot to mention that I tell people the second most important factor to consider aside from what I mentioned at the start of this post is which firearm you shoot the most accurately over your weak-side shoulder while fleeing. If there's an exit strategy available to you this becomes your new primary plan of survival.