Hands down the FI exhaust is louder but not annoying loud. The HKS is quieter at idle and during normal driving, it only comes to life at the higher rpm ranges and it's a sweet sound indeed. Either is a good choice but you have to choose whats right for you.
Check out AK's Video's
Finally Got my exhaust! HKS Hi-Power Ti Exhaust (many Pics, Video inside AK370Z)