Magnaflows are alright. I have one and its too short so my car is really loud. I also heard that they don't have much rare metals so they tend to not last very long. As far as emissions go. I used to have a high flow, metalic core cat. I liked it, but I can't remember the brand name.
18" Enkei's & Kumho Ecsta's-------UNICHIP Eibach Sport springs----------Morroso oil pan Injen CAI & Oil cap----------Stage 2 FI cams Custom Exhaust-----------TRD Supercharger AEM alt. pulley -------JSP Carbon Fiber hood 380cc injectors----DC Sports ceramic header