In reply to alasdair19:
Bit of a non-question in the sense that there is no real answer - it can be good anywhere in December, but it often isn't.
A few years ago we did routes in Val Daone, and Lago di Tovel (both roadside) first weeks of December, and so on.
Choose your venue and flip a coin.
What is obvious is that there is more chance on the northern side of the Alps, and in all places very high up. For example Circolo del Gelo, in a side valley to Val Daone, is typically in condition from November to April. Nice free bothy to doss in. But you need to plod up, preferably on skis or at very least snow shoes. It is not a short walk and you will definitely be breaking trail (plenty of mixed granite routes awaiting an ascent up there as well, just in case anybody cares).
If you come to our part of the world (near Arco) then you have the interesting plan B of rock climbing in the sunshine and eating tasty pizza if the ice is pap.
Or indeed, even if the ice is good, a rest day on massive limestone slabs in the sun.
(But not even that can be guaranteed).