Do a search on the site about this as it's been asked a few times, but the main ones people go for are scorpion, powerflow and milltek. I've just put a powerflow on mine, nice and subtle and not too loud, but it depends on who's fitting them as some people seem to complain about the workmanship, so far, touch wood, mines been fine. I'm guessing, but I think most mk2 owners will probably say scorpion.