I've told several people this, if you don't want to pay money and get a huge upgrade to sound, then find someone who modded his SS and take their exhaust. I've done it and had no problems and it sounds amazing! Totally different sound from idle to WOT and my exhaust now has the coveted "popping" sound
On the other hand, if you want the best money can buy, MRT 2.0 (not the first version) is the best option imo.
But there are plenty of other good ones too.