Reims is a day trip for me, mainly when I'm wandering the WWI battlefields (of which Reims was one.) Reims was flattened in WWI. The area around the cathedral received in excess of 200 major caliber artillery shells. WWII was slightly less damaging, mainly because the battlelines rolled past that area fairly quickly. But if you want champagne, some spirits, and excellent cheeses, Reims can be a pretty good place to visit.
If you go, remember, don't buy anything without tasting it first. Even in the wine shops. If they don't have an open bottle they'll open one, provided you are buying.
Rouen is totally different. It has managed to retain more of the old buildings, it's got a huge legacy of royal patronage, and it's got Joan of Arc. It's also a fairly busy port city, and the industry and foods are noticeably different than those of Reims. I spent two nights in Rouen earlier this year and I'm already making plans to return. I very much enjoyed my time there.
If you go, walk the garden behind the Hotel d'Ville, and don't miss the antique shops around the Cathedral Notre Dame. The Musee Beau Arts is exceptional.