This is a very difficult question. You would have to qualify the question be asking “best for what”?
There are so many different aspects to car hire that you have to consider.
The aspect which most people think of first is the price. Many people assume that best is cheapest. I can assure you that I have collection of horror stories over an eight year period when customers went for the cheapest options and it did not work out for them.
I know a company who offer very competitive prices and will take all the bookings that come their way even though they have no idea whether they have enough cars to cover the bookings.
When it get near the date of the hire and they know that they cannot cover it, they send the customer an email giving a sob story about how the car they were going to get was involved a terrible accident (or something similar) and they will not longer be able to cover their booking.
The customer then has to search about at the last minute trying to find another car hire company and ends up paying over the odds because they are late. The company concerned on the other hand have made sure all their cars are fully booked.
So the moral of the story is to use a reliable company who is not going to charge you more than you should pay.