I stayed in Vienna for five days with two friends of mine, and the Christoph's apartment was simply perfect.
The host welcomed us when we arrived, showing us the house and giving us many useful advice about Vienna, places to visit, restaurants, pubs etc..
The apartment is perfectly located, less than 10 minutes walking from the Praterstern station (S7 from and to the airport, U1 and U2 metro), from where you can reach the city center by metro in only 2 stops. The apartment is also located near a supermarket, in case you want to buy something to eat at home.
The apartment was very clean and equipped with all the stuff that you may desire (the kitchen if fully equipped with many household items).
I totally recommend the Christoph’s apartment, it's simply the best place!