As long as they are 4.0's, the one with 190K miles would not scare me, although I would perfer the one with lower miles. Its all about maintenance though, so If the higher mileage XJ has proof of a oil change every 3k miles then the miles don't mean much for the engine.
Second It would depend on rust. I am not sure where you are, but here in PA cars rust FAST. So the one with no or less rust always wins. Check for the obvious rockers and floor pans.
1998 is a good year, so if you check over basic things and they both seem mechanically sound, then all you have to decide is do you want one in good condition, or excellent condition.
1995 Cherokee Sport