An expert guide to Alpine mountain biking
Steve Mallett, author of Alpine Mountain Biking, a new guidebook, puts four places in Switzerland in his top ten: St. Luc, Crans Montana, Zermatt and Verbier.
Yes, Chamonix is there, and Tignes.
Mallett has an article on his top ten in Britain's Guardian on 18 June 2015.
From what I could judge (I'm not a biker) his advice is sound, on both tracks and accommodation.