December has the swell of November with a fortnight of Christmas on the end of it. The north-west groundswell keeps arriving with the period the reefs need, the alisios are months away, and the north shore works day after day.
The water has come down to 20°C, still a 3/2 and still warmer than mainland Europe by a long way, which is exactly why the islands fill up from about the twentieth. Before that the line-ups are reasonable. After it, El Cotillo and the Lanzarote reefs get the same crowd January will have. If you can choose your fortnight, take the first one.

