Feta is one of the more popular pairings when it comes to watermelon. The sweet and salty flavors balance each other out and the creamy, crumbly texture of the feta is a great contrast to the watery crunch of the watermelon.
They do say that opposites attract! All that aside, you can easily leave out the feta and still enjoy a delicious watermelon salad. You could also swap in goat cheese, which has a more mild flavor.