I have had almost 20 different exhaust combos on my 3 LS1s. Get an ATR or Borla.

 

Depends on what your budget is. But I like my setup. I installed a Borla exhuast, including the y-pipe. Then I installed an electric cutout that fits great where the Borla plates go. I ran the wiring to the center console ashtray where I have a small switch. Sounds great and within seconds I can send all the flow through the Borla muffler, which sounds good too. When I'm on the highway cruising, I just turn it down. The nice thing too is wide open and totaly closed aren't the only options, you can open it as much as you want. Have to say that I leave it wide open 90% of the time.