Best caliber also depends on whether or not you can actually get ammo for it currently. I went with a 9mm simply because I have a bunch of 9mm ammo and no .45ACP and all ammo is scarce right now. Otherwise you just have a pretty paperweight.
With a 1911, any caliber other than .45 ACP is just defeating the purpose of a 1911. I have plenty 9mms, but when I wanted a 1911, it had to be 45 ACP.
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