We've spent a week at Slavo apartment, and it was really cool:
+ ultra clean and well-prepared for guests
+ all possible home appliances, modern and easy to use
+ plenty of storage space for clothes and luggage
+ high-speed internet over Wi-Fi
+ good connection to public transport (bus stop accross the road, U2 stations Krieau and Messe in 5 mins, 2 Citybike stations - highly recommended)
+ close to Prater park
Please note that:
Bedroom window looks to the east, sun will not you sleep too long - but you don't come to Vienna just to sleep, right?))
All windows are street-side, so if you are ultra-noise-sensitive - be ready to hear cars noise (not too much).
Overall - highly recommended high-class apartment.