Talking “proper” calibers is the equivalent of what Linux distro is best. It comes down to how accurate and quickly can you shoot under pressure. By most standards a .22 is too light a round to stop someone, unless you can precisely hit the head and potentially multiple times. A 9mm is kind of gold standard starting point for self defence. Like someone mentioned, if you aren’t a great shot, or feel like under pressure you wouldn’t be accurate, grab a shotgun. Just racking one can stop some people from attacking.