In reply to tinkadventures:
My two penneth...The ecrins are much more spread out as there are multiple venues but long drives between. If you go somewhere for a week you would likely need to drive round quite a bit as there isn't really one venue with loads to go at across all grades.
The routes are good though. Celiac, fressiniers, la grave are all good.
I think though that cogne is a lot better for this type Of trip if you haven't been to either area as it's basically two valleys that you walk down as far as you want and pick a line that you want to do.
Also nowadays I would imagine conditions are more reliable in cogne over a wide range of route grades.
The accommodation is good in cogne. We went with a club and there were some bi apartments. Can't remember the name though.
If you've only climbed in rjukan the grades will bruise your ego somewhat in both areas!