I would say spring to fall is all good. In winter, you can have snow in the mountains, from some 2,000 m (6,560 ft) up. I will never forget how I was swimming in the ocean in Puerto de la Cruz in October, enjoying some 30°C (86°F) outside temperature while actually looking at the peak of Del Teide far up in the distance that was covered with snow already. Incredible experience.
I would say spring to fall is all good. In winter, you can have snow in the mountains, from some 2,000 m (6,560 ft) up. I will never forget how I was swimming in the ocean in Puerto de la Cruz in October, enjoying some 30°C (86°F) outside temperature while actually looking at the peak of Del Teide far up in the distance that was covered with snow already. Incredible experience.