It took some cogitatin' but, after 50 yrs of shooting the short guns, I'd have to say it's this one. That's a Combat Commander, in the pic below; made before the Series 80 trigger BS started; outfitted with a beavertail grip safety, target trigger, Wilson Match barrel and bushing, and good early Wilson sights.
It's a .45 as issued, but I fitted it out with a 9mm barrel and slide, a .38 Super barrel & slide, and a Ciener Commander length .22 lr upper. It's about as useful a .45 you can imagine...ammunition? not a problem...pick one you like and change out the upper. Practice cheaply, with accuracy that has to be seen to be believed?; stoke up the Ciener. CCW? It's a bit heavy, but if you run out of bullets, hell, you can club 'em with it. It's the last hand gun I'd sell off.
.38 j-frame. Handguns are great, but I'll take the concealability over 17 round capacity. Rifles solve the big problems. Handguns get you to the rifle or away from problems.
1) most common military pistol round is 9mm, now that even Russians use it
2) at the end times everything will cease to exist, except for Walmart
3) Walmart will continue to sell cheap 9mm
If you were to own only one gun for all of your handgun needs..it would have to work well for concealed carry, bedside and general end of the world stuff.
P5 Guy, that's probably when CC would be most needed. You don't always want people to know when you have a gun. But watch the end of the world talk. "They" don't like it. One-gun scenarios can apply to these times with financial hardship as well. I've downsized...not through financial hardship, but because there are only so many guns you can truly be proficient with.