Big chocolate fan here but my preference is for a glaze (or simple powdered sugar sprinkled over) rather than melted chocolate. The reason is that the chocolate top becomes the star rather than the brownie and in a cool room, that chocolate can become hard, making the brownie mash when you bite through it.
A glaze is easy to make and "lighter" on the brownie. Make sure they are fully cooled before glazing and then give the glaze some time to set up as well before cutting. This glaze is a lot like chocolate glaze you find on donuts....
2/3 cup powdered sugar
3 tablespoons unsweetened cocoa powder
1/2 teaspoon vanilla extract
4 to 5 teaspoons hot water (or more...)