Sounds cool i suppose abit bored of S-Systems but anyways...
The JG S-System is the best clone S-System ( In this case i dont own any personaly) Airsoft scotland say
"Given the results of the recent head-to-head between TM & Dboys in Airsoft International, there may be a new leader of the pack right here.
Having disassembled one of these recently to install a M100 spring, we can report that the gearbox would put a CA of G&G to shame! Beautifully finished incorporating steel gears, a metal spring guide as standard, chromed cylinder with absolutely no air leaks... Just awesome!"
Obviously there trying to sell the things but this tends to be backed up from what people have said in reviews.