Well, it's been a while, but I ended up staying free at a combo of Hyatt Carlton Tower (BAD) and Sheraton Park Lane (Great). I did walk by the Marriott Grosvsnor Square and it is a beautiful hotel in a lovely setting. It is close to Bond Street and lots of shopping and sights. Given the chance I would definately stay there (if I wanted to accrue Marriott points). While the Marriott County Hall gets great reviews, it is right behind (literally) the London Eye and the London Aquarium, so massive amounts of tourist tend to congregate in front of the hotel. Also it is across the Thames from most attractions (while not far, it is not in the 'midst' of everything.) I did not see that many restaurants nearby either--but I could be wrong.