I've got to go with the Model 19 Combat Magnum, the revolver that set new standards being a medium frame revolver chambered for the new, game changing, .357 Magnum.

In any barrel length, the Combat Magnum, to me and for that reason, is the quintessential example of "the" S&W "Classic" revolver.

Coming in second, perhaps the model 27, but it doesn't hold a candle to the sexy Combat Magnum.