Many purists will tell you that serving a Manhattan over ice makes a completely different drink. It is true that most Manhattans don’t include ice, but that doesn’t mean you can’t try it on the rocks. The ice melting will dilute the cocktail, which may change the flavor if you’re used to it being served in a chilled glass. Despite what some bartenders might tell you, it really doesn’t matter, and ice isn’t going to change things as much as making sure you’re getting high quality liquors and a solid cherry. In fact, some scientists argue that a little dilution can bring out whiskey’s flavor better. If you’re still getting used to whiskey, it will be even more helpful. Try it out and see what works best for you. At the end of the day, your personal tastes will be the most important factor.