I like bavauto although I haven’t heard any feedback on their springs. I had Eibachs on my E34 and really liked them. IMO since that is their only product, the quality is something that would reflect the long standing of the company. I’m not sure if price is a factor, I try to look for the best price certain things on my car, but I also factor in how long before intervals. Changing springs doesn’t happen as often as changing oil or brakes.