I personally like the angled look (N1 & HKS)- looks much more Japanese tuner like. They will all produce ROUGHLY the same gains, so it really depends on which one looks better and which one sounds better. The TRSM sounds really deep and smooth, but I really don't like the look. The N1 is more or less a louder version of the HKS, with both giving off a deep but somewhat throatier sound that the Tanabe.
Do'h, i have to pay around $500 to gain about 5hp haha...that's a waste of money. i think i rather stick with my current custom exhaust, which its sound is hella way better than all those ugly exhausts. the bad thing is i don't know how much gain i get from my custom exhaust at all.