For location my favourite would be Browns or the Connaught. Lots of great restaurants nearby and Mayfair has become a lot buzzier over the last few years. I also like the location of the Soho Hotel and the Charlotte Street hotel, although Soho and Fitzrovia are trendier and less refined than Mayfair, so it depends on the type of atmosphere you like. I agree to a certain extent with the comments on Knightsbridge above. It can be a little boring, although there are some good restaurants (I'm thinking of Zuma, Amaya and Marcus Wareing). Don't forget Sloane Square and Chelsea are within walking distance and have a bit more going on.