I have found Bluebird Servos pretty good and they are much cheaper than some of the alternatives. I don't notice any performance difference between them and the much more expensive KO servos that I also use although I'm not racing at the highest level. The ones I use were less than £30 and are available from
www.demonpowerproducts.co.uk . I have found this to be one of the best online model stores, Nick has always replied quickly to any questions, even when I was new to the hobby and didn't really know what I was doing.
Darren at DMS racing
www.dms-racing.com will always give you good honest advice and help about the most suitable kit to buy. He is an active member of this forum and his shop sells a massive range of products.
Ben