I choose my retirement pistols the same way I chose my off-duty pistols, and I have several of each in the common service calibers of 9mm, .40 S&W and .45 ACP, with barrel lengths ranging from 3", 3.25", 3.46", 3.5" & 3.75" ... and I'm about to order a Shield 9 (3.1" barrel).
Caliber isn't as high on my list of priorities as it might be for other folks, but then as a firearms instructor & armorer I do a fair amount of shooting, allowing me to maintain my skillset with the different calibers. (Recoil forces, recoil management & controllability are factors to consider, granted, which is why I do a lot of training & practice.)
Although I'm a longtime .45 enthusiast, owner and shooter, I tend to prefer the smaller guns I use chambered in 9mm nowadays.
I like my .40's because they're so similar in overall size & weight to my 9's, whereas the .45's are just a bit larger when it comes to some grip frame dimensions.
Just depends.