It depends a bit on the size of your pocket and where you want to stay.

If you want to have the most downtown locations, the IC is an obvious choice. There is a very reasonable HI (Graf Adolf Platz) in the mid of downtown. Starwood has a mediocre 4P property still in a very good location. Hilton and Radisson are more in the suburbsclose to each other, however, about 10 minutes from the towncentre by tram. Beside that there are hundreds of privately operated hotels or smaller chaines (like Lindner) not known in other parts of the world.