We stayed in Vienna for two nights over new Year. The apartment is located very close to Schönbrunn. The Underground is very close and you can reach the city center very fast. In case you are traveling by car, there is a Park and Ride in the underground stop which you can reach in less that 10 min walk and can park for 24hrs for a very good price.
The apartment itself is great, ver spacious, with a fully equipped kitchen and 2 separate bedrooms. The beds in the smaller room a a bit squeaky, but other that that everything was great. There is also a nice living room/dinning room to relax in.
Vienna is an amazing city that I would definitely recommend.