Truth be told, before doing our research, we didn't really know an Old Fashioned from a Manhattan. So we shall share our newfound knowledge with fellow aspiring whiskey cocktail aficionados:
The main difference is that an Old Fashioned uses sugar and is therefore much sweeter, while a Manhattan incorporates sweet vermouth which is more complex and bitter than sweet.
While this classic cocktail seems simple enough with just a few key ingredients (whiskey, vermouth, and bitters), it's fun to learn about the various nuances that each ingredient plays. For example, if you prefer a dry drink - go for Canadian Whiskey and Dry Vermouth. If you are looking for something a bit sweeter (without being overly sweet), try Bourbon and Sweet Vermouth. One of the best explanations we've found about the Manhattan is from The Spruce Eats, including recipes for variations on the original.