Well, I went with Borla after the the second time the exhaust failed. The Second time was with a Flowmaster. I've had my Borla fail but it's Borla sends me a new one and I send them back the old one. Oh speaking od this, I prefer bolt-on catbacks. The clamps allow me to adjust and remove parts easily. This is a nice feature if you're on the road or trail and damage it to the point where it has to be removed. Then later you'd be able to put it back together yourself.
Performance over the Flowmaster and stock was noticable.
Only Cj's have the tail pipe sticking through the leaf spring. The moved it for two reasons. One, it would send exhaust fumes into the passenger compartment. Two, it got damaged. Only a custom bend would put the exhaust there. Also, if you have a YJ, you might want to consider getting a new downpipe. The stock one is pretty restrictive and hangs rather low. Having it rerouted infront of the oil pan will allow it to be tucked up higher. It will also get rid of the kinks in the pipe. I think the pipe is around 1.75-2" rather then 2.25"
Here are some other things to consider. Get a all stainless steel exhaust. (I think this leaves out Flowmaster since their only protection is aluminized paint.) Mandral bends are smooth and do not reduce in size. Straighter is better. Less turbulance will allow for the exhaust to move quickly without creating any hotspots. Get a good warranty. Exhausts aren't bulletproof. You'll probably end up breaking it for one reason or another. Pay once now so you won't have to pay a lot later on. Forget about loud exhausts. Loud exhausts don't necessarly make power. If you plan on doing long trips or use it as a daily driver, the droning from a loud exhaust will get to you. If the exhaust is too free flowing, you'll lose your low and mid's in the torque band. You'll gain higher HP's that will only come into play higher speeds.
