I highly recommend Rainer’s place - it is centrally located, yet in a street which is very calm; the apartment is spacious, impeccably clean, and with all possible amenities. Rainer is s great host, always available and of great help with some tips (when and how to get a pass for public transportation; where to go for a good breakfast or coffee, what to visit and why, etc).
I enjoyed enormously our Vienna experience, and this was largely due to such a great hospitality!