In reply to whenry:
> We'd only be getting the lift pass for VT and Orelle, not the full Three Valleys one, unfortunately - can't do anything about that.
Surely you just stump up the extra 50 euro? Seriously though, if you go with a public group they may insist on the full 3V pass. If this is really a deal breaker then I would want to have confirmation from the provider that just a VT pass is ok. I have been in the 3V when everything in VT was wind scoured but the snow around Meribel lovely so I wouldn't want to limit myself like that.
All that said, I'd probably pick Tignes anyway, more variety of long off piste descents, although I have spent a lot more time in Tignes than VT so possibly just know it better. But Tignes + Val d'Isere trumps Val Thorens on its own pretty comprehensively (my favourite off piste is on the Val d'Isere side)