You're gonna have a good time whichever company you go with, they're both in the Tarentaise Valley afterall… best valley for biking in the Alps that I know of.
I think that tA are somewhat better placed that WR. Being in Peisey (on the picturesque side of Les Arcs lift system) gives tA a choice of whether to ride uphill from the door, ride down from the door, use lifts only (FROM THE DOOR), use a combination of lifts and pedalling, etc, etc, you get the idea… it's lift-accessed stuff, but on the edge of the backcountry, resulting in basically endless possibilities as to what a riding day could entail, and catering for all possible tastes.
Sainte Foy where White Room are is lovely, and the riding is all good but there's no lift-accessed stuff at all because of the fact that the lifts don't operate there in Summer… bit of a mission in the van to get to the nearest lift which runs…. pedalling is of course great, but a mixture of pedalling and lifts is the best IMHO 🙂