I can also give you a perspective from the other side. I too looked at the X when we got the Liberty. The room in the front,(hip,shoulder) is greater in the KJ. I know I compared both at the auto show. I was too cramped in the X. The X has more rear seating room and cargo room, however.
Towing: Based on what I read here, The KJ is a lot better. It's rated at 5000lbs. I tow my 20ft F/S Glastron(3600lbs), my 18ft RV(2600lbs), and my race car(4800lbs). I have gone across country with them and the KJ did much better than I would have ever thought; mainly due to the weight and power.
Offroad ability: Honestly, their both pretty close. The X has more clearance stock. The KJ better approach and departure-a big deal on the trails I go on. I think crawl ratio and flex is slightly better as well on the KJ.
Unibody vs frame? Of no advantage when your talking the small lfts. Don't forget the Cherokee is a unibody and will go places neither of these 2 vehicles will go when modified. Moreover the KJ unibody is light years ahead of the Cherokee in strength anyway. Although I do like being able to do a body and suspension lift on a framed vehicle.
KJ LCA hang lower,but are much beefier; take your pick.
Suspension: I prefer coil springs over leafs for offroading and clearance. But leafs can be made to do very well.
Axles? I believe the X to have a strong rear, but I wouldn't bet the farm the're any stronger than the 29 spline ones in the KJ. I believe the diameter is larger in the KJ. I race on the 27 spline one. You won't break it on measely 32s.
Quality? Side-by-side I thought the KJ used better materials throughout.
Reliability? Anyone's guess. The drivetrain is proven in the KJ, but you may get nickle and dime stuff. I'll say maybe the X for overall dink stuff because it's a Nissan.
Tom