I've done the bus trip.. and used the U-bahn.. and the taxi.. Take the taxi if you have luggage.. If you don't, take the taxi.. while Berlin's subway system is certainly decent, you do have to take a bus first to the U-bahn.. then change trains once.. while it is cheaper, it can take a bit to get to the hotel. Potsdamerplatz is the correct stop. You can't miss the hotel. It's located across the street from the Canadian Embassy. Look for the red maple leafed flags.