My first criterion is that the make/model in question must have been tested, adopted, and retained by a major LE agency or military unit. That thins the herd quickly.
Beyond that, I’m in the “carry what you shoot best” camp. After decades with the 1911, I went to a Gen 3 G19 based on advice from folks I trusted. I got a good baseline with that, then tested a dozen or so others over a period of a couple of years.
Testing meant buying the pistol and a good Kydex holster/mag carrier combination, then shooting that rig exclusively for a couple of thousand rounds, starting with slow fire and load testing out to 50 or 100 yards to baseline accuracy. Then I’d move to timed and scored drills like El Pres, Hack Standards, etc. Then I’d make the drills harder, shooting them in the dark, in the rain, while moving on broken ground, or as many of those factors as I could combine. (I live in the Pacific Northwest, so rain and darkness are easily had six months out of the year and gravel pits provide the broken ground and distance from humanity needed for shooting on the move, etc.)
One or two pistols were somewhat easier to conceal and one or two shot better in slow fire at extreme range. None were as easy to conceal or to shoot well as the Gen3 G19. Some were especially good on one drill or another, but none were as good all around as the G19, though the VP9 came very close. My issue with the VP9 was that while it grouped tighter than the Glock in almost every test, when I threw a flier with it, I REALLY threw it. Like into the next time zone. I imagine that if I were to shoot this same series of tests with my current Gen5 G19, the accuracy difference between the it and the VP9 would vanish but I'd still throw flyers with the VP9.
I shot Glocks when I took classes with Ken Hackathorn and Pat McNamara, and the VP9 for an LAV class. I also shot Glocks when I was involved in IDPA. After I learned the ropes, I routinely finished in the top 3 in local club matches for a couple of years but that probably says more about my local clubs than it does about the pistol or my skill with it.
At this point, I’ve moved from Gen 3 Glocks through the Gen4s and into the Gen5. I’m pretty sure that I’m done looking.
Okie John