No one mentioned the wonderful Maritim Hotel in Bonn. I wonder why ;-). I think the best choice in Bonn is the Hilton. It is well located in the city right at the river.. The Kameha is newer but in my opinion too far off. Yes the subway station Ramersdorf is 500 meters aways but as soon as it rains the 500 meters are pretty far.
If you need more information about Bonn please contact me.