We have crafted a fairly slow 5 week round trip which starts and ends in Lyon in May/June 2025. The itinerary to date, which I'm very happy with, has us catching our breath for a few days in Cremieu, then spending an average of 5 nights in each of northern Burgundy (Semur en Auxois), then the Jura (Arbois), and eventually 5 nights each in La Vanoise and then Ecrins National Parks before ending our trip with a few days in Lyon.

In between the Jura and La Vanoise stays, we have a final 5 nights to spend. If we detour a little into Switzerland, we could stay in the Fribourg area (we've previously spent a long time in Grindelwald and the Lauterbrunnen Valley and don't want to drive that far out of our way). Alternately, we could give those 5 nights to the Chambery area, which would certainly create a calmer and 'neater' itinerary because of the relatively small distance from Arbois and then on to La Vanoise. We prefer village or small town stays and hilly country with good walking (the big hikes will wait for the two National Park stays).

Can anyone help us decide between these two options?

I see your trip is coming together nicely. I cannot help with your dilemma. We have not been around Chambery or the two national park areas. We did visit the Vercors in 2018.
I am sure you will enjoy Arbois. We stayed in nearby Salins les Bains several years ago and it is a beautiful area. . We are going to be in the Haute Saone to the north at a similar time. and will go back to Arbois as a day trip. We plan to visit the Arc et Senans saltworks as well. We did the tour of the saltworks in Salins when we were there. You can also go down to Chateau Chalon and Baume les Messieurs which is a Plus Beaux village I think. We saw a couple of sources of rivers while we were there - the Lison was quite impressive as well as the Loue and the Ain. I am a sewer so we detoured to the small village of Nozeroy to see the straw embroidered on silk altar piece embroidered by nuns in the 17th century. The geographical features called reculees are interesting.
The Jura of course produces wonderful cheeses such as Comte, one of our favourites which can be bought at different ages , 6 months, 12 months etc, and Morbier. And of course, the lovely smoked sausages Morteau and Montbeliard which we have a few times every trip as they are available all over France. And Arbois is also a wine centre. Some places have laiteries where you can buy cheeses and dairy products. I remember buying cheese in the one in Salins and watching as the attendant ladled thick cream or creme fraiche, not sure which, out of a large tub for another customer. These are the sorts of things we enjoy about our travels.
So I am sure you will have a lovely time. I hope you come back and do a trip report on your stays as I and others enjoy reading about the different ways people travel, as well as finding new places to visit.
Bon voyage.

Thank you again, rhon, for your guidance, your great suggestions and the inspiration I’ve been getting from your posts and trip reports. Very generous of you!

I haven't been to Chambery, but FWIW, I enjoyed Fribourg. I must admit that 5 nights would be too much for me there -- but then, my travel pace is not at all leisurely. It certainly has a number of places of interest that could be quite pleasant to see at a relaxed pace.

If you do go and if you have any interest in prehistory, I highly recommend the Latenium just outside Neuchatel, about an hour or so away.

Hope that helps!

Five nights appears excessive for some places and a full week might be good for others. Aix-les-Bains would be a good destination on the Lac du Bourget.