Enterprise is a small company, and the branch near the Frankfurt East Train Station is really tiny... They only had one car available, so there was no choice. After negotiating, they gave us a free ride to the airport where we could choose from four cars. Returning the car was also hassle-free. In summary: Enterprise offers enthusiastic service and competitive prices, but they have a limited number of cars (didn't see the numerous Mercedes and BMWs as some mentioned). You need to be lucky.