Caliber debates are largely a waste of time in my opinion. The best caliber is, primarily, whatever you as an individual shoot the best; by "best" I mean quickly and accurately. A good hit with a .22 is more effective than a poorly-placed .45 or a miss with an RPG-7. J. B. Hickok demonstrated this in many a gunfight using cap 'n ball revolvers that on a ballistics chart are far inferior to a .380 ACP.
At any given time I'll carry and I shoot .380, 9mm, .40, .38 SP +P or +P+, .357 magnum, or a 10mm. With the exception of the .380 all of the other rounds are similarly comfortable to me. I'd lump .45 ACP in there too, although I sold my .45. Any differences that I feel in shooting these various calibers are negligible. The particular load makes more difference than the caliber in my opinion. I feel much more difference between shooting a standard velocity .40 and some of the hotter .40 loads like the Magtech Guardian Gold, than the difference I feel when comparing a standard velocity .40 and a standard velocity .45 ACP. That shouldn't be very surprising considering the muzzle energy of the standard velocity .40 and .45 ACP loads fall pretty much within the same range, but you'd have to shoot .45 ACP +P to achieve a muzzle energy similar to the hotter .40's. Only the little .380 feels different because the Kel-Tec P3AT is a frickin' 8-ounce gun with some sharp edges at inconvenient spots. But it is reliable and surprisingly accurate. Shooting 50 rounds through it at a single session does chew up the hand a bit, but to borrow a line (and slightly change the meaning) from Clint Smith: A gun should be comforting, not comfortable.
Of the calibers listed above, I carry .40 a majority of the time. I wouldn't feel under-armed carrying any of them. The difference in the firearms-- in terms of comfort, ammo on board, and mode of carry-- determines what caliber I'm carrying, not the caliber itself.