I first pick location close in favoring a neighborhood feeling and avoiding major streets due to traffic noise. Prefer 3* boutique hotels. My preference in London is either Kensington/South Kensington or Bloomsbury for their neighborhood feel. Bayswater, Earl's Court, Soho, Chelsea are not a nice IMHO. Piccadilly is too touristy and crowded. Mayfair, Belgravia, Knightsbridge are too expensive. I love www.booking.com because the ratings are only from verified guests and you can sort by ratings, plus use the map view for areas.