Completely different vehicles, TJ will cost more money to purchase, leaving less money to build it, XJ will be cheap to purchase, but will require a little more work. Both vehicles can be budget boosted for cheap, when it comes down to full suspension lift kits the xj will be cheaper, when it comes time for resale, the TJ will hold its value better, etc...
Just too vague of a question IMO.
TJ is a frame rig, which is a perk, XJ is unibody.
XJ's are great, I personally would rather have one than a wrangler, but thats just my experience.
I wouldn't go beyond 33's on stock axles on either vehicle if you intend to wheel it, 35's if your going to mallcrawl it.
Whats your total budget? To buy a vehicle, and to build it, this amount will help narrow down the choices.