I've already got my "1 handgun" handgun.
My 4" S&W 686 no-dash.
I am surprised that in a condition where you can have only one handgun, most people are opting for a revolver. I thought a semi would be the choice for its capacity.
Nope. And I've got the "hi-cap" bottom feeders. They're nice, but if I were to be limited to just 1, I'd want that .357 Mag wheelgun. It is rock solid reliable, extremely versatile, and with 6 rounds it has enough capacity to do the job. If I need more oomph or capacity than the wheelgun supplies it's time for a long gun anyway, and the wheel gun gives me enough capacity to fight my way to it or flee, as appropriate.
The versatility thing is the clincher. With the same gun, I can plink away with .38 Spl wad cutters that are just about as mild as shooting .22s. Accurate, too! Or, I can load it with "standard strength" .38 Spl ammo if I choose. I can load it with .38 Spl +P self defense ammo, or .357 Mag self defense ammo, my choice, no changes needed to the gun. I can load it up with heavy .357 Mag hunting/field defense loads -- again, no changes needed to the gun. I can select my bullet shape to suit what I'm trying to accomplish without regard to feeding (within reason -- speed loader and OAL issues).
Add in the more traditional, less threatening look (to the sheeple) as opposed to your "tacti-cool" polymer frame bottom feeder, and the fact that I happen to like the looks of the thing. Even though it is >only< just shy of 30 years old, it is still "old school". That counts for something, right?