For sure le Massif! It's no comparrisson at all. In fact I can't think of a single aspect where MSA would be better. Last year I didn't go to Massif until springtime because I had season passes to MSA/Stoneham/Relais. I did about 40-50 days at those hills and would trade them all in a heartbeat for a couple more days at Massif.
I think we're pretty much set on Le Massif now.
Where did you stay? Any recommendations for accommodation? I know they don't have a village, and their hotel is about 10min (not planning on taking their 'train' option as its not worth it)