I went on two tours with Pas a Pas Tenerife walking tours during the 5 days I was in Tenerife in December. Both were wonderful. One was from a peak in the Anaga Mountains to the north east of the island that ended with a delicious local meal in a very interesting village on a peak overlooking the sea, where people's houses are built into caves. The other hike was in the "La Caldera" area through the myriad colourful, small volcanoes with views out to the beautiful snow-capped Teide volcano in the distance.
If you, like me, are someone who enjoys holidays where you can hike through natural landscapes, see spectacular views, try local foods and learn something about the history, flora and fauna then these tours will suit you. The guides are knowledgable about the area and clearly are passionate about the Canaries. Ask them pretty much anything about the plants, animals and history along the way and you will get an answer.
One of the best things about the tours is that they are small and personal. There were three of us on day one and five of us on day two. This was in contrast to a lot of other tour groups we saw, where upwards of 30 people were stomping along the trails, scaring away wildlife, and being herded on and off buses.
I would particularly recommend this tour if you are travelling alone in Tenerife (as I was) and want to hike through the countryside. I just didn't feel comfortable hiking alone and the guides and my co-hikers proved to be lovely company.
The tours are easily arranged just by emailing the company (see website - http://www.pasapastenerife.com/ ) before-hand as I did. I think you can do it by SMS as well.
I would also recommend Puerto de la Cruz as a great place to base yourself in order to see/walk the most interesting parts of the island. There are economical local buses going pretty much everywhere of interest (Los Gigantes, Anaga, La Laguna, the Teide National Park). Puerto is also a pretty little town and worth seeing just on its own. The hotels are fairly reasonably priced and I even managed a self-catering apartment.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.