I buy from Morco, Silverprint and Calumet. All have given me an excellent service. Not tried AG Photographic yet, but they are on my list to try.
I do have to say I can't fault Silverprint's service and advice. For me it has been outstanding - especially when I do my anorak bit at the counter. They certainly had the patience of a saint when I called in a few months ago, as I wanted to see samples of all the photographic darkroom papers they had. I was there for hours and didn't spend that much in the end - but wow what a service I came away with a good feeling and some great papers to try.
Service doesn't get better than that!