Mod: Downpipe

Need help on choosing the best downpipe for my WRX, but one that isn't annoyingly loud.

You need to start by clarifying what you mean by "best". Best HP gain, Best build quality, best cost performance?? Best set-up meaning bellmouth vs. separtated waste gate, etc.?? There is an awesome write-up on downpipe on NASIOC forum, I can't find it, but you may want to look....it's worth looking for. I'm not sure that different downpipes make a huge difference on your exhaust sound...at least if you have a stoct cat-back, any DP shouldn't make it annoyingly loud.

PDE, TurboXS, Invidia are all really good bellmouth DPs
HKS flange style (covers wastegate partially) is proven to be just as effective as the bellmouths with absolutely no possible damage done for half the cost