I only did a bit of research myself and what I found was:
The Stg 2 are great and dont really require springs. But they make your valves float above 7400 or something crazy. So after a long period of time you might have enough wear for something to fail. Also the BC dont need gears either. But from reading the cams arent "on point" stock like the S4's and S3's are. You have to dial them in with cam gears for them to reach there full potential. So in reality I think the S4/s are actually the better deal in the long run...The BC's arent really drop in cams like everyone thinks.