You might want to have this thread moved to the 2011+ v6 section for more replies.
I would say that if you don't want raspiness stay away from an off road x pipe. I'd stick with the long tubes, a prochamber or h-pipe and the axle backs.
I have heard the Roush axlebacks on a 3.7 with factory manifolds, cats etc. and they sounded pretty good.
12 Black GT500 SVT PP l 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.