No IRS or IFS on the Grand, Its live axle Front and rear. I know, I'm Jeep guy. Live Axles are what make the G.C. so great, but the ride does suffer some comp-ared to the Liberty, which does have Indipendant front suspension. (yuck)
The X is a radicly diffrent truck from a Jeep, either the cherokee or the Grand. Both the Cherokee's are smaller, roughly the same size. they are unibody construuction, but have extreamly stiff chassis ment to handle yeahs of hard off road twisting and stress. This makes them feel exceptionaly responsive to any steering or throttle imputs compared to a body on frame truck like the X.
The Jeep's motors are either the 4.0 inline 6, which is one of the best non deasle torque motors ever produced, or the 4.7 V8, which is a decent, light weight and powerfull, if basicly unremarkable motor. The Automatics are built to handle the extreams of off road use, and are heavier duty than those found in other SUVs of this size and weight, while the Manula Xmissions are varried. The AX-15 is stout, but the syncro's will wear fast, the newer NP3550 has a higher first gear, and lower torque capacity, but is still a 1 ton truck transmission, and isn't going to break unless you tow 22foot trailers up mountians with 44 inch tires and a lead foot as you take it over a fallen tree.
Axles are a diffrent story. the front Axles is almost always a Dana 30, with Dana44 knuckles. its stout, and hard to break even when your trying to. It can handle the full sustained torque load of the engine, but as a front axle, it never has to.
The rear axles are either the corprate 8.25, the dana 35c, or the dana 44. The Dana 35c is junk for the most part, but it does ok in 2wd's that won't see off road use. the 8.25 has axles as thick as the Ford 8.8, and is a good axle. The Dana 44 is nearly builet proof under a jeep.
The Ford Explorer is a medium weight SUV, 1000 heavier than a Cherokee, its larger, with more interior space, and a floorboard not compromised by the need to tuck the transfercase and fuel tank up high. The flatter floorboard also means it has less ground clearance.
The X had several diffrent rear suspensions over the years, ranging from leaf springs and live axles, to coil sprung independant suspensions. All of these rear suspensions ride comfortably, none of them were ever very stable, as they were desined for comfort only, and there is some truth to the tales of Explorers rolling over. Try getting a trailor at a U-haul, and you may find they have a policy of not attaching trailers to Explorers.
The Live Axle version used the Ford 8.8 Axle. A very stout Axle able to handle more power and torque than the Explorer would ever see. Infact, the Axle is so good, many hot rodders and Jeepers use the Axle in there project cars as an alternitive to the only slightly stronger and much heavier Ford 9 inch.
As for powertrain on the explorers, I am not the expert on the diffrent motors and transmissions used, but hey, they're ford, right?
Alright, thats alot of information, and it basicly boils down to this. Which will she prefer? WHat will she be using them for?