We stayed for a month at Marlies's place in the 13th District of Vienna (Hietzing), and had a great experience!
We were 3 adults and a one-and-a-half year old baby. Both the apartment and the neighborhood was just right for us.
The apartment is at the top floor of a large house, owned by Marlies's family. It is large, lots of natural light (with complete darkness in the bedrooms if needed), underfloor heating, with top quality appliances, furnishings and furniture, and very clean!
The neighborhood is quiet, clean, green (though the winter had started when we arrived), and felt very safe and child friendly. There is a nice playground in Hügelpark, which is nearby. Also in regards to transportation, there is a main tram line 60 within close walking distance, and a subway station (U4) that you can reach with the 60 or after a 10 minute walk. And.. Schönbrunn :)
Communication with Marlies was just great! She was responsive and kind with us!
We will definitely come again! :)