When I booked this hotel, the main reason was that I had an early train to catch from the Westbahnhof to Germany. Unfortunately, after my booking, in the new time tables the trains to GErmany don't leave from the Westbahmhof anymore. Fortunately, the Meidling Bahnhof is also easily reachable with U6.
The hotel was just off the Westbahnhof and the entrance is on a small side street. Still, it was easy to find. The hotel itself was very big and my room was facing the Gürtel, but still only on a few occations could I hear the traffic through the windows.
The only poblem I had with the room was that on three out of the four days I stayed at the Mercure my room key didn't work and I had to return to the reception to have it activated again. Since I had a busy schedule and had to run back and forth between my room and the reception (about 5min in one direction), it was very disturbing. Also the personnel at the reception never appologised for this.
Apart from that I was pleased with the hotel; wifi was working just fine and for the everyday errands the location was practical (near U3 and U6 + a couple of tram lines).