A .22 makes a poor defensive round. Sure, it kills but do you realy want to wait around for 4 hours for the guy to bleed out?
Unless you can get very close and place the round into the brain or vital organ, the .22 kills by slicing through the body much like a knife. Most deaths from .22 are from the internal bleeding that is caused by the round.
The object in self defence is to stop the intruder FAST. All of the larger caliber pistol round are fine for this.
Better is a shot gun. Even bird shot at close range will stop most people. A pump action is farly cheap and easy to handle.
Keep the .22 for target practice.