Which route out of Lyon?

Can't help with that question, but you might also want to take a look at ViaMichelin.com . It uses green to highlight especially scenic roads, and I see a lot of green offshoots from both of the routes you mention. If you will have time for a detour or two that day, you'll have lots of good options. You'll need to zoom in to see the green.

I assume your are not flying into Lyon on an overnight flight and planning to drive to Chamonix the same day.

No, we will be arriving via TGV from Paris after five nights there. Thank you for the tip.

In my opinion, both routes are fine, even though I think the southern route has somewhat better scenery as you approach the Alps.

One distinction is the RCEA (Route Centre-Europe Atlantique) -- this is a designated major trucking route between Central Europe and Atlantic ports in France (from north to south: Nantes, La Rochelle, and Bordeaux).

While portions of both of the routes Google Maps has presented to you are part of the RCEA, more of the northern route is (all the way to just south of Bourg-en-Bresse), whereas the southern Google Map route leaves the RCEA southeast of Geneva. Because of this, one could reasonably expect to be driving among heavy truck traffic (semi tractor-trailers; in French poids lourds, or PL, which means heavy weight) for a longer distance on the northern Google Map route than on the southern one.

If you're curious, and even if you don't read French beyond knowing that "mort" means dead, peruse this website on news articles about the RCEA. Most of these incidents likely occurred on two-lane stretches of the route than Autoroute style stretches (similar to U.S. Interstate highways), but still. Interesting things happen when you have truck drivers from a dozen or more different cultures driving the same route along with autos, buses and motorcycles. This one is especially interesting: last year around this time I remember the local news reporting that a driver plowed into a group of 30 to 40 wild boars who exhibited poor judgment by scheduling a staff meeting on the RCEA one evening around 11 PM. Fatalities included 11 boars and what appears to have been a Peugeot 208.

Back on topic: In addition, if you add in the traffic around Geneva (lots of folks work in Geneva but live in France because it's cheaper), you could also expect more auto traffic on the northern route than the southern route while you're in the Geneva metro area. This would be especially pronounced if your arrival time in Lyon leads to you hitting Geneva around the morning or evening rush hour.

In summary, I would probably pick the southern route, all things being equal.

However, I would recommend, a week or so before you arrive in Lyon, to check the government's Bison Futé website, which provides information on current and anticipated traffic problems including construction zones. If one or the other route appears to be having major construction work, factor that into your choice. (Try to ignore the cute little Indian mascot on Bison Futé -- the French aren't exactly the most culturally sensitive when referring to members of Native American tribes).

Good luck! Chamonix is a very memorable place to visit.

Bob, thank you for that thorough response. Good to know about the heavily congested routes with truck traffic. Given that it will be my first time driving abroad, I’ll take the longer route with fewer trucks over a faster route. The Pennsylvania turnpike is bad enough.

Your comment on the boars’ meeting made me laugh!