Stock is best. But if you just want it to sound cool, Flowmaster super 40 and magnaflow hi flow cat. Here's my bud's 02 TJ with that setup. After having it for a couple years, he's playing with going back to stock. You don't gain any power from doing ANY type of exhaust setup. Only power gains you can get out of the 4.0L are with turbos, superchargers, stroking the motor or swapping in a V8.
But on some of the exhaust I've looked up it adds quite a bit power to it. But i am a rookie at this jeep stiff so thanks for the input
They usually just put that as a selling point. Honestly it really doesn't do all that much except give a more aggressive sound. Maybe it'll feel like more power because it's louder, but it's really not doing anything.