Luton were great for me; they spotted that I was routing around them from Duxford to Blackbushe, and invited me to track through their airspace! Farnborough must be one of the busiest and are usually excellent; they've been running a survey recently on the quality of their services, so you get the impression that they care what we think.
With Solent it seems to depend on who's on duty...it varies from excellent to 'not very tolerant' in my experience.
Bristol always seem to be friendly, very clear (the most important attribute for me) and sometimes humorous (a particular lady controller makes me want to go back to Bristol just to hear her dulcit tones).
So far, I've never been refused clearance, but I guess there's always a first time.....