While I like, and have, both calibers, for my situation I find 45 cal to be better suited.
I am also a good shot when calm and focused. Shot placement is not a problem for me when conditions are good.
I haven't had much practice or repetitive drills with my adrenalin pumped and my heart racing. By all accounts, these factors make pinpoint aim problematic.
You are still responsible for rounds that don't go where you intend them to go. I live in a residential area, and high velocity small caliber rounds that miss the target will go through several walls and still have enough energy to severely injure people. This is what 9mm will do easily.
Ball ammunition is a military projectile made for maximum penetration in whatever it hits. I don't want these in adjacent rooms of my house and certainly not my neighbors, whether it passes through the intended perpetrator, or not.
Therefore, I chose a large caliber frangible rounds as the first ones to come out the spout; Like the Glaser Safety slugs in .45 caliber. These are a fairly light rounds, Basically a copper cup filled with steel shot and a plastic nose that spreads the cup and the shot right after initial entry. Penetration of a typical interior wall leaves fragments with little velocity and not enough energy to incur lethality. The wall is screwed up, of course. And, rounds that do hit the target don't exit. So, injuring someone behind the target is very unlikely.
Yes, 9mm is cheaper than 45 Glasers. But, 45 Glasers are still cheaper than a funeral... or lawyer fees for wrongful injury suits.
If you think you are a good shot, run in place for three minutes and then check your shot placement/groups within 15 seconds. Try it. Have someone else time the run and see how many rounds hit your target in 15 seconds. If someone is advancing on you from seven yards out. You have less than 15 seconds to stop them.
The .357 round was developed in 1934 so police so they could shoot through gangster car doors. These penetrate like .38 Super and both have better penetration than 9mm.
If you must have a 357 auto-loader, find a Coonan, or a Desert eagle that chambers that caliber.
There are frangible rounds available for the 9mm, too. Extreme shock and Sinter fire come to mind. You tube has several demonstration videos of these. I haven't fire them, though.
After I use up the Glasers in a fight, the plan continues with Golden Saber and Black Talon, then Federal Hydra shock, and 185 Gr hollow points. These have all been tested to fire reliably in by defense guns.
In summary, the wider the swath the projectile makes, the more energy will be expended in the initial target, minimizing risks to non-combatants.
Of course, I'm assuming I won't have to defeat personnel wearing vests or armor. If I'm expecting these, there is always the .50 AE or .454. They'll need 3/8 to 1/2 steel plate to stop these
But, these really aren't routine carry or quick to action guns.
Cheers,