Ten page thread and still no caliber war--I'm pretty much amazed.
If I had to choose just one of the 3 it would definitely be 45ACP. I'm 60.
I carry both 45 and 40 on the rare occasions I don't carry 10. I find 40 is an acceptable smaller round shootable in a very compact carry gun when I need to do that, and my 45 is adequately compact (M&P 45c) for most other times.
40SW is a good cartridge for me for loading lots of ammo cheap for IDPA ESP division practice and I've found adequately accurate loads for it. It has been tougher to work up accurate load/bullet combinations than for 45ACP in my experience.
I like handloading both because case size is reasonable for observation and handling with fat thumbs, and both can be loaded down with virtually identical powders and charges of Solo 1000, Clays, Nitro 100 and so on.
I have never warmed up to 9mm and it doesn't fill any perceived 'need' that I have..any gun I'd like to own is available in 40, 45 or 10mm, and if isn't available in 10mm I'm probably not much interested anymore anyway.