Hi!
Heading to France in November and while we will spend the majority of our time in Paris, going to add a two night stay elsewhere at the start of our trip. I've narrowed it down to Metz or Chartres. We will arrive at CDG mid morning and then train to the town and stay two nights. I've found lodging options in both that are great, and I think which ever city we do not stay the two nights in, we will visit on a day trip from Paris later during our trip.
I've read lots of posts here (which were so helpful to confirm both are great places to visit)! The Christmas Market in Metz is a huge draw as well as the Illuminary in Chartres (which given the time of year looks to start around 6pm, so make the day trip option plausible!)
I think either way we go will be a great success - just always appreacite the splendid feedback from the forum :)