First of all, the place: Serge has a neat, clean flat in a prestigious neighbourhood, very close to transport links. The room is furnished with an extremely comfortable bed and a small, useful desk.
Most importantly - the host. Serge is a very considerate and helpful host, provides useful advice for all your needs when staying in London. Apart from being a host extraordinaire, Serge has amazing people skills and, if you are lucky enough, is a great company for a lunch or a pint!