We have done this trip numerous times both ways, as yet although the traffic around Paris has been busy we have never been stuck unlike Lyon where we have been caught in a traffic jam for 5 hours so beware of when the French decide to decend on the south of France!  The best thing we did was invest in a SatNav and if you go via Paris the sights are great and you also get to go over the Milau Bridge, further south, which is spectacular and there is a viewing area there where we try to stop and get a coffee and stretch our legs.
Have a good trip!