All depends how much noise you want. Milltek resonated is quietest, Piper loudest... mongoose somewhere in middle. Janspeed dont make ST exhausts any more, nore do Magnex. Scorpion are cheap pn Ebay but there are not many of them fitted on here. Both Profile/Wolf and Performance Deals UK have offers on exhausts at the moment, and as mentioned drewamscience have just released a new design of cat back whichI think is built my Blueflame.... So you choose how much noise you want, them pick your price and tips....
Mark