Personally my bottom is .380 auto/9x18. I prefer the 'big 5' duty calibers of .38spl, .357mag, 9mm Luger, .40 S&W or .45ACP due to their abilities, proven performance and availability. I would consider anything that is as/more effective, though, if price/availability was considered acceptable. Say .357sig, .45GAP, 10mm, .44 special, etc
Right now I only have .38spl +P, 9x19, .45 ACP and .357 mag.
And as for the oft repeated "a .22 you have is better than a .45 at home", well, yeah, duh...but I try not to make decisions like this based on them being better than the worse possible choice. If your choices are a big .45 at home or a .22 in your pocket then you are, IMO, doing it wrong.