Mules are my favourite to-go shoes for the spring and summer, as they carry both comfort and elegance, and are extremely versatile. I like to think that during a hot day, I can kick off my shoes in a single movement (it's also extremely practical for security lines when traveling). Also, the lack of a sling in the back avoids the painful burns on the back of the ankles that come with new shoes, or any worn for extensive periods in hot weather.
While mules are also known as "slings" in English, and a search for the former term on popular online shoe retailers yields very little results. Being the ever-French and proud Francophile that I am, I still prefer the earlier term, which, in French, is also used to designate a very stubborn person (such as a toddler, but not limited to) with the charming expression: "tête de mule."