Difficult to add anything new to the other positive reviews! I've stayed in Vienna many times and this was quite outstanding. Aside from all the details others have highlighted, Christian's sheer professionalism was impressive. There was a problem with the WiFi. He both responded and sorted the problem very quickly. His communication is excellent. It gives you confidence.
The actual street is less than impressive - as is the entrance hall - but once you reach your 4th floor apartment, it's a different world. Really well equipped - especially if you're self catering as I was.
The proximity of supermarkets, trams - 3 stops to Westbahnhof and Schonbrunn palace and gardens a few stops the other.
Stop looking. Book it!!