If you go to Vienna, I highly recommend staying at Gero & Lisa's place.
The apartment is really conveniently located - I rarely had to spend more than 15 minutes on my bike, 20 minutes on Vienna's excellent public transport, or 30 minutes walking to get to where I wanted to go! The area has some really lovely cafes, coffee shops, and restaurants within walking distance, as well as several supermarkets, etc.
The apartment is really excellent - it is very spacious for a 1-bedroom apartment with heaps of storage and a really well kitted-out kitchen so you can cook a nice meal at home. The shower and laundry are excellent as well, and the heating keeps the place very comfortable in the colder months, and the fan and airflow keeps it comfortable in the lovely Viennese summer. The internet, too, was very fast!
Lisa was an excellent host - I had a few questions during my time there and she was always quick to respond. Key pick up and drop off were convenient, and I felt very well looked after. What else can I say? An excellent place to base yourself in Vienna, whether you are staying for a short trip or a longer trip like myself. Thanks again Gero and Lisa (and Laura)!