What is your definition of off-road? What do you want to do with the car?
The X5 has many limitations off-road, but can handle dirt roads and the odd grass patch easily. But wheel travel, ground clearance and attack/departure angles are road-car-like.
Disco? Which one? Disco 3 does fine on- and off-road, but air suspensions are a very well known problem, and don't even try to use "afrika-diesel" (diesel mixed with anything to make it cheaper, mostly paraffin), you will kill your injectors on minutes. So north Namibia/Angola/Zambia/Tanzania/North Mozambique is out.
(We had to help a Disco at Purros that drank Africa-diesel.)
Who the hell said Jeep??? There is a reason why they depreciate quicker than underwear! Talk to any mech at a Jeep dealership and they will tell you what are common problems(Gearbox, diff, etc.) Not cheap to fix.
Prado's do well on and off-road, they are reliable and many parts available.
Fortuner's have the same qualities, but a bit more crude inside(not a bad thing off-road), also likes acrobatics... Newer diesels don't like africa-diesel, but might get way with it in the Fortuner, but just take note.
Pajero is a unsung hero IMO, it has very good on-road manners for such a capable off-roader. The DID diesel is near bullet-proof, I have seen untouched engines with 430K km and still going strong. Most say the engine is good for 350K at least. It will also take bad fuels without problem.
One thing to note, the Pajero has independent rear axles, so loading the car lowers the ground clearance and departure angle a lot, esp if you tow a caravan. I would recommend Old man Emu HD springs to lift the car a bit(+- 5cm) and decrease rear sag. I have personally driven with one over Van Zyl's Pass(google for images of the place) without much fuss.
So, what do you want to do with the car?