What is the best hotel to stay at in London?

What is the best hotel to stay at in London that is not too expensive (more than 400 dollars per night) but not cheap. I want to stay in the best location.

Brown's Hotel, Albemarle Street, Mayfair

The K West hotel in Olympia is lovely http://answers.yahoo.com/question/accuse_write?qid=1006052523397&kid=NbUvWDC0WTFHmubgxeIx&s=comm&date=2006-05-28+18%3A26%3A06&.crumb=