Hi, booked 6 or 7 times from sixt Dubai, as a Diamond member, and always book a MB C class only once was upgraded to MB E class, all other times was upgraded to MB C with bigger Engin!! From C180 to C200 or C240 (what a joke) as the say no cars available and one can see at least 20 MB keys in the locker. The Diamond discount was good. Gave up and moved to Avis. Booked Audi A4 and upgraded to A8. (Avis president circle).