It all depends on what you are defending yourself from and where you are doing it. For bear country nothing beats a 12 guage pump loaded with 1oz slugs.

For personal carry protection from two legged pretadors I like the time tested 158 grain SWCHP FBI load from a .38 caliber revolver. It's easier to get on target for a followup than a magnum. A .44 special or .45 Colt with a Keith load is also a good choice.

If my job included breaking down drug dealers doors I would want one of the plastic fantasic bottom feeders in an easy to shoot but good man stopper like .45acp or .40 S&W. I believe the 9mm to weak and the .357 sig and 10mm too hard to control for a fast second shot.

This opinion and a buck fifty will get you a cup-o-coffee.