The best gun is the one you hit the target rapidly and accurately with be it a 9mm, a 40, a 45ACP ,or whatever.

If you have to actually shoot a single perp, don't just shoot once and watch, shoot 'em like a singer sewing machine while moving,starting at the chest and zipper up till they are not a threat.Have a b/u mag and a flashlight if possible.Perps probably have partners, so look for his buddy.

I refer to "people" defensive handguns. When outdoors for protection I carry a Ruger Bisley 45 LC with hot loads for penetration.Almost had to use it on a black bear once.

You gotta use what works for you.Practice alot!!.