Well I'm from the school of thought that the number one rule in surviving a gun fight is "have a gun". So if it was a choice between 22 mag or nothing I'm taking the .22 mag. Most home defense situations are stopped without a shot being fired, someone breaking into a house isn't looking for a gunfight they are looking for a victim. If you point a pistol at them chances are they aren't going to stick around long enough to determine if its a pellet gun or a .44 magnum. The second rule of a gunfight is that if you need to shoot someone, you better be able to hit them where you are aiming. as Col. Cooper used to say "a .22 in the tear duct is much more decisive then a 9mm in the wishbone." To answer the original question the gun most often used in crime I think would be the "saturday night special" small revolvers. They are short, cheap, and easily concealable which makes them the best option for criminals (which is why they are often demonized...unfortunately these same features make them great self defense guns).