Whiskey: Morgenthaler recommends “cask-proof bourbon”, especially Booker’s. Booker’s, as far as I can tell, is expensive, when you can find it. His alternative recommendations are Old Grand Dad 114 (~$30) and Stagg Jr. (~$150?).
Original recipe calls for a teaspoon (5mL) of 2:1 simple syrup. I find it plenty sweet without this addition.