We used PepeCar last year when they first came out. They only had brand new Mercedes Clase A cars. Nice cars, handles well, and fit our luggage better than bigger cars that we've rented before. Don't let the size fool you, it was roomy. And we are a family of 4! We will definiately consider them again when looking at rates for this summer.
One thing though, they say they are at Barajas, but their office is not inside the terminal. To find them, you go outside and catch the little minibus to long term parking, get off at the parking and they are right across the street.
Hope this helps.
K. Sanchez