I don't know about any of the other exaust systems, but I installed a Borla Dual exaust system and thourghly enjoy it. It is not quite as loud as I had expected (I have had 3 others on Z-28 and SS Camaro's and it is by far the quietest) but I was very impressed by the extra power that you can actually feel. As far as better gas milage, I cant keep my foot out of it to tell. O by the way, it took 45 minutes tops to install.