I’m not sure that it is necessarily the most versatile cartridge, but a revolver chambered for the .357 Mag. is an almighty good all-around handgun.
Ammo is available with bullet weights ranging from 110 to 180 grains, and for the handloader, bullet range is even wider. Many people use speedy 125-grain bullets for defense or police work, but I would argue for more weight—140 to 158 grains—to get the job done.
In addition, 180-grain loads are great stoppers and a guy with a good Magnum revolver and a supply of them could keep himself fed in an emergency.
Above all, the .357 has a huge advantage in that it is also a .38 Spl. and the range of ammo in both calibers is simply enormous.