Open 2" Drag Pipes. Hands down. My friend had them, and they were LOUD! I could hear him coming about a mile away. He didn't care about performance, but that bike sounded WAAAY Cool when it fired up. I have 1 3/4" drag pipes with 1/2 baffles, and my bike was a lot faster. lol!
And I believe that Drag Pipes are popular because they are so reasonably priced. Right around a Hundred Dollars at a swap meet. And they do sound sweet. You can baffle them to your taste, or leave them open and suffer a small HP loss, but no one can argue that they dont produce power at top RPM as well as most other pipes. So if you like to accelerate WFO they may be the ticket. They are easy to ceramic coat on the inside before you mount them and then they don't turn blue for a long time if you do it right.