I had a fantastic stay at Stefan's; the flat was nice and in a very happening area packed with cool bars and shops. My room was great, spacious, quiet and very comfortable. Stefan is not only the perfect host but also one of the nicest people I have ever met :) He helped me with everything I needed, showed me around the area, acted as my interpreter, helped me get a German sim card... I don't think I could have picked a better place to stay in Berlin. Highly recommended.