All handguns are relatively poor 'stoppers' regardless of caliber or bullet used. Shot placement and sufficient penetration are paramount, all else is secondary.
Barring a hit to the CNS, the only way to stop a determined & aggressive BG is shutting down the brain due to blood loss.
However, even a solid hit to the heart can leave 10+ seconds worth of oxygen, plenty of time for the BG to do you serious/lethal harm before he expires.
All handguns underperform, some underperform worse than others.
With that being said, I EDC 9mm as the best combination of controllability, effectiveness & capacity but I don't trust it (or any handgun) to reliably stop a determined & aggressive attacker.

Tomac

All other things being equal the .45 will be a better stopper, not by a huge margin though.

This being sa8d the 9mm is easier to shoot, holds more rounds and is far cheaper to buy so you can practice more. These thing make it generally better for the average person. The main thing with a handgun is to hit the vitals. Most people have a better chance of this with a 9mm.

This topic made me think of this. LOL

https://scontent.fslc2-1.fna.fbcdn.net/v/t1.0-9/12348098_1068327316551715_5452763912415594767_n.jpg?oh=d2de1b90f10ecfd67febb082b3a45227&oe=58E23B11