We've always rented through rentalcars.com, they offer good deals from a range of suppliers. Agree with the full-to-full and taking own excess insurance, look at the various options regarding extra-drivers, Budget tend to include it. Rental company excess policies often exclude tyres, underside etc so watch out, the policies you take independently usually include these.
When you pick up ostentatiously take photos of the car, inside, outside and the mileometer too. Have these in your hand when you return it. Good luck.