Richard: Sir; my understanding; for the word 'best' becomes a relative term.
Each situation requires circumstance, situation, relevance. You can walk into about any USA "country store" and purchase ammo. .22-.38-.357-.44-.45-270-30/30 30-06 Through out the world this will not work. In a battle field, what ever you pick up when you need something else; USA has created 1 dominate battle field round; this eliminates part of the problem created by 'war situation' for USA
The 9mm round is world wide, will that make it the best?
As I prefaced; 'best'; becomes at best; ammo/equipment availability at the time of need. Too; being able to pick up something off the ground to fix your weapon; will that happen? The nine fits somewhere into this classification. Shoot-ability opens another can of thinking.
Credence given to anything, anyone as 'best'; David killed Goliath with a slingshot and a rock.
My take; "survivability will take demonstrable ablility to take what you find and make it work"