I don't have a bike, but I do know, if you want a loud exhaust, get the Growler,
Jardine GP1,
Competition Works GP Slip-On,, or the
Hotbodies MGP Growler.
No idea which is loudest, but my guess would be the Jardine GP1, since it's pretty much just a straight pipe. Any slip-on is louder than the stock exhaust.
Loud pipes are usually cheaper.