In Rheims if you want affordable but gorgeous go to hotel de la paix. It is actually a best western but it is in the heart of town and all the locals rave about it. Of course there are the castle hotels as well like the crayeres etc. but those are more than double in price. We booked through Amex and of upgraded to a suite at no extra cost.
In the Alsace I had got recommended the kanzel hotel and residences. This was my favorite location of the trip.