We really enjoyed our stay at Volksoper apartment. The place has a pleasant decor, is very clean and spacious, and has everything you need and some more. The ring and most major sights are easily accessible by public transport. If you like to walk (we do!), it's about 15 minute walk.
There are number of places to eat and drink within short walking distance, and a kiosk with middle eastern food, which stays open very late.
Peter is a great host, and let us in earlier than his check in time.
We highly recommend this place.