The worst thing about .40 is that the brass looks too much like .45 when I'm scavenging at the range.
The best thing about .40 is that was consistently available in stores during the last panic.
Because of advances in bullet technology I no longer believe that there are dramatic differences in terminal performance in commonly available defensive calibers.
With simple barrel switches and a .22LR conversion unit for its top end, my SIG P229 does .22, 9mm, .40 and .357. There is no compelling reason to give up .40, but will never bother to reload for it, or 9mm for that matter. Availability drives my choices.
My carry guns are .45 ACP, but only because I shoot it well, and I will always reload for that to keep practice costs as low as possible.