Picking a muffler for someone else is like trying to pick a girl friend for them. Personally, I don't like my Jeep loud so my preference is a Dynomax Super Turbo. Gives you a little deeper sound but not too loud. Still have the stocker for now but it's starting to rattle so probably will have a Super Turbo installed soon. Some folks like the Flowmaster 40 series, sounds good but somewhat loud. Or you can go with a Flowmaster Super 40 series that sounds similar to the 40 but doesn't have the drone that the regular 40 has. Only problem is it is a 5" case instead of 4 so you'll loose a little clearance. The Super 44 is similar to the Super 40 but has a 4" case like a regular 40. Some folks like the Magnaflows. I have a good friend that had a 98 4.0 with a Banks cat-back system on it when he bought it and it sounded great and was not obnoxious inside or out, but a little louder than a Dynomax.