My vote (like a lot of others it seems) goes to Farnborough Radar..as well as being generally cheery and friendly, they are also cool under duress, as witnessed by myself a few months ago when I heard them helping a recently qualified PPL (who had taken friends for a spin), in making a successful forced landing after an engine outage.
Additionally, the London Information guys/gals are surely worthy of a mention for their generally friendly and composed manner, given the massive coverage area and on occasion extremely high workload - this combined with sometimes having to deal with with some of the most appalling R/T I have ever witnessed. Well Done! You are not always appreciated...
WxJx