"Best" has too many variables for any one of us to make a clear case for all uses and conditions. Not unlike the concept of what's the "best" oil, toothpaste, audio speaker, cell-phone plan, etc.
I don't believe there is any one "perfect" item that fits all situations. You must choose based upon your perception of what's probable and/or possible.
Conceptunally, the "best" carry gun is the one that you can shoot with a high degree of accuracy, and still put the largest, fastest round down-range, without over-penetrating the target, and have the weapon concealable for carry. That is a fairly concise description of the "best"; it's firearm uptopia, if you will. Unfortunatly, it's also often impossible to attain because of all the variability in each individual scenario. Some are human factors; others are environmental. So you compromise with what meets the largest probability, while minimalizing the other undesired possibilities.
Consider:
How well can one shoot a given weapon/caliber?
What kind of environmental conditions (weather, light/dark, rain, etc)?
What kind of physical barriers between you and the target (clothing, doors, media, etc)?
What type of target?
ETC, ETC, ETC ...
One of the most difficult decisions to make is how to deal with winter, should you be in a region where that season presents it's challenges.
Example: You must select a weapon/ammo that can perform to the stated criteria against a 30 year old, 280 lb threat dressed for 5 deg F temps (heavy coats and shirts) because you're walking back to your car after a sports game on a Friday night, and yet not have that weapon/ammo over-perform when you walk into a resturaunt 15 minutes later and meet a completely different 19 year old, 135 lb threat wearing only a tee-shirt. It's not likley you'll stop to change out ammo or weapons; you're looking for the combination that will provide its value for the greatest amount of presentations, with the least amount of potential risks.
My peronal favorite? Glk 29 loaded with CorBon; nothin' says "cessation" like a 10mm with around 600 or 700 ft-lb of energy (ammo choice dependent), when you can consistently put it where it belongs (center mass), and know that it won't over-penetrate. This combination works for me; I'm large enough to conceal/handle the weapon, and have it succeed in a great many circumstances, with the least risk of failure, including acknowledgement of civil risks thereafter. But that only applies to me. Look at my wife (small, demure) and a .380 is "best" for her.
You have to determine what "best" fits those same criteria for your blend of situations. For some people, it's a .45ACP; others like the .38 in +p; others perfer the 9mm.
There is no "best" for all people, nor all situations. There are "better" choices for individuals when presented with the most likely situations.
It seems to me that you understand these criteria, because you acknowledge the subjective nature and challenges in your post. So, it's up to YOU to decide what's "best" for you, not us.
