If I were going to tow another vehicle, I'd seriously consider a Durango with a 5.2 or 5.9 engine. The XJ and the ZJ are unibody vehicles. The Durango has a separate frame to which a strong hitch can be securely mounted.

An XJ or ZJ may have been strong enough to deserve their tow ratings when new. But when considering a 15+ year old vehicle, corrosion could weaken the inside of the unibody "frame" effectively reducing the real world towing limits of the vehicle. The problem is that such internal corrosion can sometimes be difficult to detect.

Edit: Whatever vehicle you purchase, read up on towing with that vehicle. SUV's usually have towing packages available. I would purchase one that had the factory heavy duty towing package.