OK, lot's of ways to play with this drink if you so choose. First, use a bourbon that you really like. I really like Knob Creek or George Dickel in this drink. Knob Creek for the depth of flavor (cut nicely by the soda water), and Dickel for its woody, oaky flavors (again, cut nicely by the soda water). I know, Dickel is a Tennessee whiskey, not a bourbon. But's its good in this drink.
Now, you can also add a dash of bitters. Try Angostura or Orange Bitters.
Last, try a twist of orange or lemon. Yum city.