one caliber instead of one cartridge, I'l go .452. That allows revolvers in .45acp, .45LC, .45AR and a variety of 1911s and other semi-autos in .45acp...I could even sneak .45GAP in there if I were so inclined.
If I were limited to one cartridge, it would be .357--J/K/L/N frames, and a Connan 1911-ish semi-auto.
It's a do-all cartridge for handguns for both SD and hunting, and performs in carbines as well for a longer shot if the family needed to be fed in a SHTF situation
Even though being somewhat new here, I will throw out an opinion. The .357 would be my choice because of the versatility being able to load up and down. From the light loads in the 38 to the heaviest of loads available in the 357. Similiar to the 270 in a rifle load.
Can run it up to +p+, keep it basic at standard pressures, throw it in various SMG, carbines and handguns. For anything other then the biggest game,ie;deer and smaller, it would be able to feed me and protect me.
I could use it in LOTS of different auto's and also in some revolvers. It wont break the bank to keep stocked up on ammo. And with the new +P+ rounds, I think it would get the job done. not to mention all the other 9mm loadings out there.
If I could only have ONE handgun, I'd chose a .357 revolver, and also shoot .38's out of it.
and myself would pick a 9mm as I am assuming the current ammo situation (price availability) would remain the same - but would pick a 357 if I hunted with a pistol.