I've been issued the 38, the 45, and the 9.
The nine is fine. Have stopped several large, agressive dogs w my nine minimeter.
The city issues the 9, the county the 40, the state the 357 in Glocks. State is switching to the M&P357. The 45, mostly in 1911s, is a popular option w the city.
Over the last 10 yrs, the 9 has been stopping as well/better as the rest. The most multiple hit failures to stop have come from the 40 (none w the 9/45). The most extreme failure to stop w one shot COM was from a 45. The 9 has had no problem stopping through the normal tactical barriers (furniture, interior doors/walls, auto glass, etc). Go figure. I'm sure many have war stories that show the flip side. C'est la guerre.
All the ammo companies can give you 9mm ammo (std and +P) that penetrates enough and expands reliably.
Not concerned w energy; more on that end means more on my end too. Not concerned w capacity; it's gonna be over one way or another before I get past six. Know of plenty of shootings where more than 6 didn't do the job, but none where six couldn't do the job.
More (bigger, heavier, faster) is better. If you can do more w more, have at it. I can do more w less.