Spoilers for Wonder Woman: Evolution #1!
Although most DC Comics fans tend to compare Superman's speed with Flash's, they neglect to put him in a fairer competition—a race against Wonder Woman. Diana and Clark can both fly and have similar sets of flying abilities. Even if Superman and Wonder Woman each have varying speeds depending on their respective solar power and magical abilities, they usually fly at around the same velocities.
Everyone knows Superman gets his flying abilities from Earth's yellow sun, but how exactly does Wonder Woman fly? In Brian Azzarello and Cliff Chiang's New 52 Wonder Woman run, Wonder Woman's ability to fly is explained. In issue #12, Hera throws Diana's friend, Zola, off of Mount Olympus. Hermes, who's helping Wonder Woman, plucks one of his feathers from his heel and throws it to Diana. As soon as the quill pierces her thigh, she gains the ability to fly and saves Zola.
In Stephanie Phillips, Mike Hawthorne, and Adriano de Benedetto's Wonder Woman: Evolution #1, Superman teases Diana into a race. After a battle with Silver Swan, Diana meets Superman on top of the Himalayas, where they talk about her latest run-in with Vanessa Kapatelis. Diana vents to Clark how she wishes she could help Vanessa. Superman consoles his friend and tries to cheer her up when he says: "last one to Everest and back is a rotten egg!" Wonder Woman follows him, and they're seemingly neck and neck. Eventually, Superman slows down when he hears a tsunami. Before Clark cuts the race short, Diana is about to say, "it's no fun if you let me win!" This statement implies she knows Superman wasn't trying.
For a short time, Clark and Diana dated in the New 52, allowing fans to compare their powers more frequently. In Superman/Wonder Woman #1, by Charles Soule and Tony S. Daniel, Wonder Woman encounters a hurricane in the North Atlantic Ocean. Wonder Woman saves two naval soldiers, but she gives them to Superman. Even as his younger, New 52 self, Diana tells him, "you're a better flyer than I am." Even if Diana is a humble hero, her priority is always to tell the truth.
Even if Wonder Woman admits she isn't as fast as Superman, it would still be interesting to see a straight-up race between the two. Flash and Superman arrange several charity races; it would be a great idea to allow Diana to test Hermes' maximum speed against her teammates. In terms of covering long distances, Flash is faster than time, while Superman has reached levels faster than light. Even if Diana barely achieves lightspeed, it is vital to note that Diana's instinctive reflexes are much quicker than Clark's, making Wonder Woman a much better combatant. Wonder Woman is able to deflect bullets with her cuffs, while Superman usually just stands there with his fists on his hips.