Google up Doc Roberts' ballistic testing and recommendations, pick one of the choices for your caliber, fire at least 500 test rounds without malfunction, and drive on.
Most of the development work of the last 20+ years has been in auto-pistol calibers (9m/.357sig/.40S&W/.45ACP) as opposed to revolvers, and there are good choices in each. The difference in performance between good choices in any of those calibers is little if any. A good argument can be made that the cheapest round (typically 9mm) so you can shoot more in training is the winner, and some very savvy people have made that choice. It has also been noted that generally, shooting performance is better with the 9, and since placement is WAY more important than anything else, that also argues for the 9mm.
In revolvers, I tend to carry WC (.38 snubby) and SWC (.38 other than snubby; .41). A revolver in a pistol caliber gets one of the choices from Roberts' recommendations. In 9mm (940), the Black Hills load with the all copper Barnes bullet; gold dots in the .45 ACP, just as with the auto-pistols in that caliber.