I’ve only been to the French Alps once but it was such a good experience I’m dying to go back, and I’d do it exactly the same second time round – Bourg d’Oisans.
You’re surrounded by classic Tour de France climbs, Alpe d’Huez, Galibier, Col du Telegraph, Col du Glandon, Croix de Fer, and then there are lesser known climbs scattered about as well, Col de La Morte, Col d’Ornon, La Berarde, Col de Saurenne, and plenty others.
Bourg itself was great, we pretty much returned to the same bar/restaurant every evening, stayed in a beautiful family run cyclists chalet called ‘Cycling Ascents’ whose owner (Kevin, I think) is a super rapid local cyclist who can do guided rides in the area as well.