I stayed with Gerhard and Nicole over the Easter weekend. The apartment is in the 7th district in Vienna and would suit a solo traveller or a couple. Gerhard and Nicole also rent other larger apartments in the same building.
I can't recommend the apartment highly enough :) It is bright and super clean with everything you need for your stay and more. The location is perfect - the 7th district is very trendy with some interesting vintage shops. You can walk to the main shopping street (Mariahilfestrasse) in 5-10 minutes (via some lovely streets and squares) and to the Ring (Volkstheater, Museumsquartier) in 5-10 minutes -there is also a bus outside the door which connects you with Vienna's amazing transport system. I travel to Vienna often for work and for private reasons and this is my favourite apartment so far. Highly recommended, I will be back :)