It doesn't get more classic or reliable than this. The original definition of cocktail was simply "any combination of spirit, sugar, and bitters". Hence, as more and more "cocktails" came to be made and defined, this formula became known as the "Old Fashioned" way to make a cocktail. So while it may have been old fashioned since at least the 1850's, it remains as alive as ever. Nowadays it generally implies a base of American whiskey, and we prefer rye for it's bold and spicy complexity that always works well in a cocktail. 

Kit includes: Green River Rye (750 ml), Liber and Co. Demerara Gum Syrup (375 ml), Bitter Truth Old Time Aromatic Bitters (200 ml)