I'm not sure what will make the 3.7 liter sound the best, but I like the flowmaster type mufflers. They ARE very droney if you dump before the rear axle, I had it dumped for one trip to the grocery store and quickly rigged the stock tailpipe back on with the resonator cut off. The farther back the muffler is and the farther back the exit is, the less sound you have in the cab. Those extra bends to get over the axle quiet it down a lot too.

I like mine a lot now, it sounds perfect. When I have more cash I will get a full dual setup just like Varners with the 2 flows welded together, but I will exit out the passenger side before the tire.

 

With my 3.7 I don't have any muffler or resonators. I run Spintech Free flow cats and straight pipe with it coming out before my rear passenger rear tire. It sounds nice and deep with no drone up until about 32-3300 RPM's and then it sounds ricey lol.