Was a cheap but anyways really good in any way possible option. I rent a transporter of the bigger class drivable with a "normal" drivers license (B or 3 it is I believe) twice. I had the Mercedes Benz Sprinter and Volkswagen Crafter in Darmstadt Nord.
The employees were friendly and capable, the cars were in a good condition and the conditions were really fair. Only minus would be, that where the cars are parked at has some distance to the service building but that was acceptable, too.
In a nutshell I am very satisfied with Sixt in all points, will most likely directly go to them next time, too, and would recommend them.