For the love of god, please don't get this exhaust. Here is a pic:
http://home.mpinet.net/primeai/gsx_exhaust2.jpg (warning: its big but not too big)
That orangish stripe around the exhaust tip, that's not dirt, or orange juice, or brownies. That's rust. I've could kicked my exhaust tip, and come close to breaking the tip off. Believe me, I've thought about it many times of just doing it. Around the canister is the same way. The exhaust is roughly 1.5-1.75 years old.
As for most popular, Apex N1 and Thermal are very nice. If you have a FWD the GReddy EVO is nice, as long as you have the money. There are other ones out there, in fact:
http://www.dsmtalk.com/forums/showthread.php?s=&threadid=65055 is a old poll for which exhaust we have.
Apex N1 has a nice downpipe+test pipe that bolts up nicely.