You want the best? iON's is the best. Only problem is the cost, but you gotta pay to play. It's hands down the best system out there. It's the only full 3" that I can think of right now, and you can get it with a highflow cat. iON's system replaces the s-pipe which most do not. I'm not sure of any others you can currently buy right now that replace the s-pipe. Essential Speed is coming out with one, and hiboost is apparently going to release an s-pipe piece for us, but they never replied to my pm about it. If money doesn't matter, go with iON.
~brian