never driven that area of france.
Lol mate, you're pretty much driving the length of the country aren't you?
uplink's route is good, but seriously...avoid Paris unless you're driving around it after midnight and before 6 am. Using A roads, it will be at least two day's drive (if not three, depending on the number of drivers) and you'll be more tired from having to concentrate a bit more. Also, you only need to hit the wrong town at the wrong time and traffic can actually be bad in parts of France (contrary to what everybody will tell you).
So it's all down to time and money innit? If you fancy getting off the beaten track and staying a few nights here and there, then A roads it is but for speed and fuel efficiency, then Peage is your only man.
How about a bit of both...do the first half of the trip on Peage and then as you get towards the Massif Central, get on to the A roads and see a bit of France that few other people ever bother with...stunning villages in the forests etc...nice bit of the country.