I would not take the X9 bus (even though it is quicker). As it only stops at the Ernst-Reuter-Platz U-Bahn station and the Zoologischer Garten S+U-Bahn station. Both of which are a considerable walk from the Hampton. So you would have to connect to another bus. The 109 bus has a stop that is only a couple of blocks from the hotel (Uhlandstraße U-Bahn station along Küfurstendamm).