I'd go with 357 magnum. Pretty much everything comes in that caliber. Everything from snubbies to the workhorse Ruger Six series, to classic Smith and Wessons. For that matter I could even throw a carbine into the mix.
Not to say I wouldn't miss other calibers, but life wouldn't be all that bad.
Not to say I wouldn't miss other calibers, but life wouldn't be all that bad.