Well I have had both on my GTS. My TRD exhaust was nice but the horse power gain was very minimal. Then I customed my own dual exhaust and the gain was nice. I havent had it dynoed yet, but i can grab rubber in 2nd gear with ease, and with the TRD that would very rarly happen if at all. If you decied to custom your own make sure you do a little reserch on the tip you are buying. Get one with a 2.5 inch inlet. And as far as price, as long as you do not do duals they are about the same.
I've heard something about dual exhuasts being bad on a 4cyl. car because there was not enough air being let out from the engine, resultin in too much back pressure or something, the conversation was very long ago, and i do not recall the terms and everything used, but it was quite interestin... haha, i didn't understand the mechanics behind it then, i still don't (partly because i forgot most of what was said). Anyone care to take a shot at this? Steven?