Get whichever one you can get the better deal on. There's not a whole lot of differences. Stock exhaust on the 12 has an "interactive valve" that opens & closes at certain throttle positions while the 9 doesn't, helps in bottom end torque. Go to Buell.com to check them out. Most will tell ya though, not a whole lot of difference on the road. Again, whichever one you get a better deal on is the way to go. Good Luck and you won't regret it. [up]