I'm running a Flowmaster 70 with a turndown. It sounds great and I believe it's also what Kolak recommends. Make sure you specify 2.5" pipes, even if you aren't replacing the manifold yet. If you get a header in the future it will save some money over having all the pipes replaced.
Also, if you get a turndown put on, make sure they add an exhaust hanger near the end so all the weight isn't on the pipes/cat/muffler.
'97 ZJ, 4wd, 4.0, 3" Pro Comp lift, 31" BFG MT KM2s, JKS Front & Rear trackbars, JKS Disco's, Rear Aussie