Blitz Nur Spec, Apex'i N1, maybe a Greddy EVO like me.

It depends on what you want. You are probably best off having a custom setup done by Nate. It will be cheaper and you can pick how loud you want it. If you want to go JDM style there are several options like I listed. You can always have a stock WRX setup put on for a small bump in performance and sound.
JC