the basic platform is about the same. even the newer xj's have coil springs all the way around. the main differance is the overall length the gc is a bit longer for more passenger comfort and cargo space. another differance is you can get th gc with an 8 cyl and full time 4wd. I would however avoid that route, the full time 4wd transfer cases tend to wear alot out quicker. i get around 14-18 mpg in my xj which is an 89 and that is all city driving. you may not get 18 but 14 is a common average. I would think your best bet would be one with part time 4wd and the 4.0. do not howevwer buy one newer than a 98 or built after 5th month of 98. the head on those was weak and prone to cracks,they also didnt produce as much power. the best was 97 to 5th month of 98. those had the most power and the stronger head castings.

they are close to equal off road,concedering they are unibodied vehicles. the coil springs allow more wheel travel than leaf springs do. and heck of a lot easier to change if needed. the only other advice i can give is make sure it has a dana 44 or chrysler 8.25 rear diff. the dana 35's was prone to breaking. either one would be fine, xj if space for cargo,or passengers isn't impoartant and zj if it is

good luck