I had the same dilemma as you as I started my flying at Biggin Hill which was mighty expensive. I changed to Rochester which meant I had to change instructor, aeroplane (C152 instead of Grunman), and surface (Rochester is grass). However, I haven't regretted it. My instructor is great, I am now used to the Cessna and I am saving loads of money!- It now costs £120 per hour with no landing fees. I am also on circuits and the savings alone on landing fees is worth the change. I need all the practice I can get! No doubt the circuits are less busy but that suits me at present and I prefer the friendly atmosphere of a smaller airfield.
Good Luck on your choice.