Whiskey is a broad category of distilled spirits made from fermented grain mash, which can include corn, rye, barley, and wheat. Bourbon is a specific type of American whiskey that's primarily made from corn (at least 51%) and aged in new charred oak barrels. This gives bourbon its signature sweetness and rich, caramel-like flavor. Rye whiskey, on the other hand, is made predominately from rye and typically has a spicier, more robust flavor. The choice of whiskey or bourbon in your Manhattan is really up to you and your taste preferences. Rye whiskey is the classic choice, but many people enjoy using bourbon for its sweeter notes. Feel free to experiment with different varieties to find your perfect match!