Which is best for me: the Tarifa Transparente without the Price Guardian, the Price Guardian, or the Tarifa Constante?

It depends on your profile and preferences:

• Tarifa Transparente without the Price Guardian: ideal if you don't mind the price varying and want to take advantage of the cheapest market hours with no extra cost.
• Price Guardian: ideal if you'd rather know in advance how much you'll pay per kWh for a specific month and want protection against sudden market spikes, with the flexibility to activate it only when it suits you.
• Tarifa Constante: ideal if you'd prefer a permanently fixed price, with nothing to manage month to month and no additional monthly fee.