I don't own a .357 Mag., but a couple of them are on my wish list... Looking at .357 Mag., it looks like the most versatile caliber ever made...
From paper-punching, to self-defense, to small/medium game hunting, and pest/varmint/predator control; I can't think of a better all-around caliber than .357 Mag.
Make your case for any other caliber, but with the Coonan/DE pistols, numerous revolvers, and numerous lever-action rifles; the only other calibers I can think of that can shoot in this variety of guns are the .22LR and 9mm, but the .357 packs much more punch than the other two competitors.
I guess if I were limited to one non-shot caliber, I think .357 Mag would have to be the one.