Use what you shoot the best, functions the best, and you have the most confidence in.
I have most confidence in .45 which is why I carry it. My father? 9mm. Neither would make anyone staring down the barrel laugh. If your shots don't go where you need them to then it doesn't matter if its a .22 or a .500 magnum..
Carry whatever you shoot best and practice practice practice
"If you show up to a fair fight, you're not prepared" -Unidentified Marine Sniper Instructor
"The philosophy of gun control: Teenagers are roaring through town at 90MPH, where the speed limit is 25. Your solution is to lower the speed limit to 20."
- Sam Cohen