A good friend with a 250f told me that either mxa or dirt bike did a shoot out of all pipes. I believe the Yosh had the best power but high $. The best value was the Dr. D, which my friend bought (loud!) and he's happy with it. Go check the library archives. It was just a couple of months ago.
Personally, have a Big Gun on my KLX and love it. Runs great, fit perfectly, and priced right. Know of others using their stuff and are very happy. Give Big Gun a call...they are very happy to talk bikes there.
Mark