We will be driving from Paris to Colmar. We will overnight in either Nancy or Dijon, before heading to Colmar for 2 nights. Which is more interesting/nice for touring around in the evening or the next morning for a few hours? We are a family of 6 with older teens.
It's been so long (1995) since we were in Dijon, that I don't feel qualified to comment on it. I do, however, consider Nancy to be a jewel of a small city. The main square, Place Stanislaus, is gorgeous; and I can't believe it's quiet at night. Why don't you check the TripAdvisor section, "things to do" for each town and see what appeals?
What I most enjoyed in Dijon (same era as Rosalyn) was following a self-guided walking route with a map from the Tourist Office. As the former seat of the Dukes of Burgundy, the architecture is quite rich and "French." The Musee des Beaux Arts (free) also represents that time well, especially the beautiful sculptures on the tombs of the Dukes.
I personally preferred Nancy to Dijon, but some of the things I liked in Nancy (museums with fine glassware, and self-guided walking tours of Art Nouveau neighborhoods) may not be available during your time frame there, and/or may not appeal to you or your teens. So I agree you should look at things to do in each place before deciding.