The Vienna Plaza is superb! Every year I do a long weekend just before Christmas to do Christmas shopping and take in the wonderful Christmas markets around the city. Every year I return to the Hilton Plaza :-))
The Vienna Danube Hilton was previously a Crowne Plaza hotel and is a fair distance outside of the city.
Some other forum members have recently written about the Vienna Plaza:
http://www.flyertalk.com/forum/Forum57/HTML/000437.html
http://www.flyertalk.com/forum/Forum57/HTML/002944.html