In reply to Owen W-G:
Wynd Cliff - the warmest crag in the Wye Valley on a sunny winter's day, although the most popular routes (Questor and Cadillac) are shaded by yews and don't see as much sun. For maximum sunshine, go for the Left Hand crag in the morning (from Papillon rightwards - The Don, Sinew and Fibre) and in the afternoon go for the far right-hand end of the Right Hand crag (especially Shaft and Klute).
Goblin Combe is also a good suggestion - along with Wynd Cliff (and its Quarry) and Brean, the only fully south-facing crags in the area that I know of. The Goblin King is brilliant, Smaug the Dragon good but not quite in the same league, and Gundabad is very pleasant in a Shorncliffy-type way. However, in the depths of mid-winter, I think the higher crags (Orthanc, Arkenstone and Eagle Rock) are probably warmer as I'm not sure the sun actually gets to the bottom of Owl Rock at this time of year(though PK probably knows the conditions better than me).
Rick