Before I tell you which I recommend I should state that on this board when it comes to exhaust there are alot of different oppinions on which is best. The big three of choice are the acrapovic link on top of one of board pages. the muzzy and the hindle.
if you go to the 12r forum and go back a little or if you start exhaust question you will notice how heated it will get. So it sounds like if you get any of these you should be happy.
I have never read anywhere of anyone being unhappy with the acra.
Minor complaiints with Muzzy
The Hindle puts out big numbers and is what king and cowboy use.
Search the archives and forum for exhaust and you will learn more than this.
Best bet since they are all comparable is to see if you can find different people with each one you are interested in that way your ear can choose the best.
I am personally saving for the hindle but if I see a good deal I can afford i will buy the acra.
hope this helps.