Good time of the year to go. Did this a few years ago right after Thanksgiving and it was excellent. If you're going up the standard route from the hut, don't bother with ropes -- it is just a long snow slog even though it is on the Jamapa glacier.
Any one of the outfits working out of Tlachichuca is probably fine. Most people go with Reyes -- we didn't, but I can't remember whom we used.
The new climbers hut is very large and very noisy. The three of us opted to sleep in the old, small 6-person hut which we had to ourselves. Kinda dank and dusty, but quiet.