What it really comes down to is what the gun is intended to be used for? I myself like bigger bore guns in general. I do have a couple of .22s for small varmints but like 9MM or bigger for plinking. So if the owner/shooter is into cheap plinking a .22 is fine. Or you can enjoy blowing banana holes in paper with a 500.
If your talking self defense? That's a whole new ball game.
IMO you can toss this "one shot kill" nonsense in the garbage. It takes a very practiced shooter with a lots of rounds down range to make that happen. Takes a certain amount of courage if the bad guys is trying to engage you at the same time. In a situation like that the very first thing that happens is you will experience a MASSIVE adrenalin dump which is going to instantly increase your heart rate. To about 120 beats a minute. That's full on exercise rate. Go run 1/4 mile, stop and instantly pull your gun and start shooting! See how well you do. So in the end size matters. A shot that puts a bad guy down wounded is much better than them standing there a flesh would returning fire. I kinda feel that unless you are real close a 380 can get you killed. Heck for EDC I'm not a huge fan of a 9MM. If God forbid I ever get into a situation like that I'd kinda like the be the winner. I will admit that 9MM has vastly improved sense the US Army adopted the 9MM but we went from one shot with the .45 to double tap with the 9. Just my opinions. Flame suit on!
Rick
Ready? Aim! I agree! Wait, wha? Ohmigosh,whatistheworldcomingto!? Time to buy a lottery-ticket!
My 'start' into online gun-talk, years (and years, AND YEARS

) ago was on a Forum dedicated to SCIENTIFIC research into terminal-ballistics, real-world ACTUAL shooting statistics boiled-down to study what calibers, platforms, loads, etc would contribute to 'one-shot-drop' effectiveness. This wasn't 'one-shot kill' mind you, but destroying nerve-bundles, musculature, and bone in a person's arm tends to remove them -usually- from active threat-assessment radar.

Well, I was a dedicated 9mm fan then, but ultimately zeroing-in on the 10mm Auto cartridge. To my unhappiness and chagrin, 9mm wasn't making a great showing, as I recall. Great control for follow-up shots in quick succession, a necessary consideration in any real-world shooting "event." For that reason and that reason alone, 9mm still validated itself, beyond that it WAS a minimum-threshold caliber. As Rick stated however, 9mm has come a LONG way. I trust it more now than I did then, I think. But, .380? I try not to be critical, because for many reasons I feel it is not my place to put it down (including the concept that the .380 cartridge has likely had some forward strides similar to those of 9mm), but I personally will not even own one, no one in my household does either. The 'kick' of a .380 isn't that much less than a 9mm, and there are plenty of lower-power offerings for training and familiarity, and while the 'power' of a 9mm isn't much more than a .380, but getting into REAL statistics and research, it is enough of a difference between effective, and NOT.