I was apprehensive about renting from Sixt because there were some negative reviews, but I was able to rent a much nicer car for the same amount of money. After I booked (using rentalcar.com I found my rental would be cheaper booking through their website) I received an email to speed up the check out process. I filled this out. When I arrived at the check-in, I had the key in my hands in three minutes. By Far this is 3 times faster than any other rental company I have ever dealt with. I went down and jumped in my car and drove away. It was great, exactly what I expected.
My only suggestion would be to do a very thorough walk around and be sure to point out any issue before you leave the garage. They do a very careful walk around including a full inspection of the windshield. They found a scuff on one of the wheels that I did not note when I picked up my car. He asked me about it and there was no mark on the tire so he did not charge me for it. I do think he would have tried if I did not present a logical case against how it could not be a recent scratch
I will probably never rent from anyone else since these guys have such a great price, service, and cars.