Only you chose your electricity rate
The most important thing when talking about electricity rates, is that you are clear about the following: you choose which market you want to be in and you can always change your mind. You choose what rates you're going to contract and you decide if you want to change to another rate or even, to a different electrical company.
Just as many people don’t know what their rate is, others think they are obliged to have the company that sends them bills always be the same. That’s not true and you are absolutely free to do what you want. Stay with the same company your whole life, or change at your whim. It’s up to you.
The only advice that is valid when deciding on a rate is that you are looking for the one that is most appropriate for you. That which is best suited to your consumption profile. That which will help you save and consume electricity more responsibly.
How to know what your electricity rate is
The first thing is to know whether or not you are in the open market or regulated market. In the case of Endesa bills:
If it says Endesa Energía S.A. Unipersonal, you're in the free market with Endesa: