Didn’t need anything particular this time, so I booked the cheaper “lucky dip” (surprise car, CCCC category), noting in the remarks that I’d be driving quite some highway km, a degree of comfort and fuel economy would be welcome but size did not matter. The friendly agent had read my comments, and offered me the keys to a BMW 216dA Gran Coupé with M Sport pack and Live Cockpit Navigation Pro. It returned an average of ca. 4 liters / 100 km. I guess it helps to have Platinum status (I book a car with Sixt more than ten times a year), but in my experience the Sixt Brussels offices are consistent in their professionalism and customer orientation.