If you plan to rent a car we recommend that you rent the car from the rental company web and not from other webs to avoid third parties if something happens during the rental.
Comparison websites, like Pepecar, should just help you to compare prices.
Cicar, Top car, Gold car, Auto riesen, Pluscar are among the most common companies.
NOTE: The main roads are safe and good, but some roads are quite steep or full of curves (mountainous landscape).
IMPORTANT: Do not leave valuable items visible from the outside. Tenerife is a generally safe island, but thieves can be found everywhere (and attractions and viewpoints where there are many tourists are more tempting).