Speaking strictly from a caliber perspective, there are loadings in both 9mm and .45 ACP that can be reasonably expected to expand and penetrate a minimum of 12" when fired from short barrels. Six of one, half a dozen of the other. Take your pick.

I chose the .45 Shield over the 9mm version for one reason and one reason only: Ergonomics. The former just fits my hand better. Had the latter been made in the dimensions of the .45 version, I would've chosen that instead.

My view is that in any plausible self-defense scenario, we're more likely to run out of time before we run out of ammo. That being said, I think we should carry what works "best" for our perceived threat level. If a J-frame fits the bill, great. Feel undergunned with anything less than a G19? So be it. There are no "one size fits all" solutions to personal defense.