We had a brilliant experience with the letting manager at Walker Wyatt. In fact, the best service I've received from any letting manager in London in the 10 years I've been here.
Our (now) landlord was initially not keen on renting us a furnished property where we could keep cats. Our agent, Stella, asked him to take into account our (excellent) refererences and managed the situation so we could rent the property we wanted. Several minor mishaps have occurred since we've been in the property - a leaking roof, need for council inspection and a faulty boiler. These problems were all dealt with quickly, professionally and with excellent communication to keep me aprised of what steps were being taken, and in what time frame, to rectify the situation.
I can't recommend highly enough the service I've received from the lettings manager at this agency... if ever I need to move house again I will definitely endeavour to find a property let AND managed by this agency.