peco - generally poor quality, exhaust note varies with back box choice
janspeed - s1 = good quality, nova rasp to the exhaust note
magnex - very good quality, a little quiet in general
scorpion - quality equally as good as magnex, louder in noise, but not too much
sportex - generally poor quality, very nova like sound
supersprint (race system) - very good quality, very very loud
supersprint (street system) - above average quality, similar in noise to the magnex
k-tec - debateable quality, loud deep exhaust note
powerflow - depends upon dealer
ALL ABOVE IMHO, FROM MY EXPERIENCE