I spent 3 great nights in Vienna in Sandra's flat, located on the border of Neubau/Josefstadt (I think?). The apartment is off of a moderately busy street and entirely silent. The furnishings are quite nice, hot water works perfectly, and all in all it's a very comfortable place to stay. It's in a nice location, although the immediate neighborhood isn't specifically charming.
I highly recommend Felzl Bakery, 200 meters up the street, Burger De Ville (serving burgers out of an airstream by the 25 hours hotel) and for those of you coming in the warmer months, Veganista Ice Cream (most flavors aren't vegan!)