I have spent almost 2 months in Sybille's flat due to a German course, and it was one of the best experiences ever. My room was cosy, bright and enormous, and the flat itself very charming. The area is safe, surrounded by amazing small shops, well served (tube/tram), although I must say that I preferred walking than taking means of transport...in less than half an hour you can reach the centre, and also the Belvedere, the Schoenbrunn, the Hundertwasserhaus and the Donau are in a walking distance (of course if you really enjoy walking for hours and discover the true soul and atmosphere of this city, which is off the beaten track). Coming back to my stay in Sybille's flat, as people who choose this kind of accommodation know very well, it's the host/hostess who make the difference, and Sybille has made it! She has a natural kindness and makes you feel at home as soon as you get in. She brought flowers in my room on a regular basis, we had some beautiful walks and interesting chats together, she was never invasive, helping me with my poor German and being nice every single day for 2 months.
I hope to have the opportunity to go back to her place again in the next future!

P.S: there are also 2 sweet and mellow cats living in the flat :-)