They're both BHS, I honestly have never ridden at them - but Summerhouse is more professional I find with bigger facilities, and Barton end is just your average BHS riding school! Barton is probably better for hacking, and Summerhouse probably better for lessons!
I think they both have websites - well I know summerhouse does as they do a lot of BD and BSJA
Bourton Vale Equestrian Centre is about 20 mins away (Bourton on the Water)
Talland is the closest though, there is another one locally but I can't remember the name, seem to recall they had a website with lots of spelling mistakes