We stayed at the Darlington Hyde Park: http://www.darlingtonhotel.co.uk/ and I would stay there again. It was affordable, clean, very safe & close to the tube.
Rated 65 out of more than 1000 hotels on tripadvisor: http://www.tripadvisor.com/Hotel_Review-g186338-d214639-Reviews-The_Darlington_Hyde_Park-London_England.html.
Have fun!