I would proably go with Turbo XS, they have very good reputation. APS arguably makes the best parts for our cars. They also make some of the most expensive.

Nick

 

for making power when tuning, your best bet is a TBE with 3" piping the whole way, with or w/out a high flow cat.

For a catback, they all make similar power...

my only mods on my '04 STi are Tanabe SMR catback (for WRX, 70mm/2.75" piping), and JDM STi panelfilter, and it sounds great, deep and throaty.

I had this catback on my WRX, and I still love it.

You can get the Tanabe for the STi with 80mm/3" piping as well.

Tanabe is known to fit really well, and is also well-made.