If you plan to stay in Tenerife, then please choose the North part of the island. Much more interesting from any perspective - landscape, history, natural beaches, food, hotel prices...
The South is a McDonalds-ready tourist place. I remember telling my wife to wait for dinner till 10 pm - at this time we were back and all cards had switched from English to Spanish, and - believe me!- prices divided by 2.
The sand in the south is artificial as well which makes all beaches the same.
In the North you'll be able to do kayak fishing, rock fishing, or surfcasting into rocky areas where there's much more fish.