Its pure opinion. There are some that REALLY put out more power than others, but youre sacrificing things like sound. It really depends what you want out of your exhaust and what you pland on doing with the car when it comes to choosing.
Personally, I dont like overly loud exhausts(for an everyday driver/autox car), or big fart cans. I opted to get the TurboXS stealthback (used with heat coat for 415 shipped) with the TurboXS axleback and I absolutely love it! Its got a really nice rumble to it at low RPMs and REALLY comes alive at WOT.
Again, remember its all opinion when choosing. If you want to find a nice exhaust thread, check out Nasioc.com and look into unabombers FAQ section where he tests like 80 exhausts.