Welded is always better to avoid those annoying leaks, but a clamp will do the trick if you are looking for a quick, cheap driveway mod. It's really hard to go wrong with a muffler on an XJ, just keep your cat in place and almost anything sounds good behind it. I have had a cheap turbo muffler and it sounded great, then a flowmaster, also sounded good but a little too loud for my taste. And currently I have a DynoMax UltraFlo and I love it, just the tone I was lookin for. It's all a matter of taste, it's tough to make a 4.0 sound bad IMO!