Choose the right side
Tenerife's tourist centers are located on the North and the South center of the island. The Northern area, Puerto de la Cruz and surroundings, already a popular destination for centuries are much cooler and have more rain, but they also have more green vegetation. In winter, the average age of tourists there is 70+, mainly people who enjoy walking on the promenades only.
The Southern area, starting at Los Cristianos, Playa de las Americas up to Adeje, is relatively new and still growing. The weather is fine, during my two weeks there I did not have any rain or clouds and temperatures up to 27 degrees, but wind sometimes. The South is more fashionable, much younger but does not have to offer nice natural vegetation. Anyway, in my opinion, it's the much better choice.