Pot luck with the Canaries. Know someone who spent last Xmas in Egypt. It was warm enough to swim (low 20s) but cool in the evening. Depends on budget - the Caribbean will be hot.
I've been to Tenerife for the last 3 Xmas' (Playa de Las Americas) and have found it to be pleasantly warm during the day (low to mid 20's).
During the night I was quite comfortable walking around in jeans and t-shirt.
December is the wettest month though, followed by November and January. If you're going for a week, you might get lucky and it might not rain a single day, but from past experience, expect a bit of rain for a day or so.
http://www.holiday-we...om/tenerife/averages/
I agree Tenerife is about the nearest for the sun in winter. We were there a couple of years ago for two weeks for the New Year. Very warm and sunny, no rain and better than being here in January. If I could afford it we'd go to Australia for the winter.