Both Namur and Dinant share a lot of similarities so there’s really no need to visit both. Especially if you’re only in Belgium for a limited time, you should choose to visit one or the other based on your interests.
Namur
Namur is an excellent day trip option from Brussels. It’s only about an hour away, has an accessible train station, and it’s loaded with a rich history. Despite its small size, Namur is actually the capital of Wallonia, the French-speaking part of Belgium.