Well, I would say that they are both good offroad vehicles but I the Montero(Pajero) has the following advantages for off road situations,
The Montero has a monocoque chassis which provides a lower centre of gravity. This does not mean that it has less ground clearance than the Prado. Higher does not mean better ground clearance. A lower centre of gravity makes the vehicle more stable and less likely to roll when tilted or driven over uneven terrain like deep rutted tracks. The prado has a ladder frame chassis which makes higher and increases the centre of gravity.
The Montero has Independent Rear Suspension(IRS) which tucks the rear differential high up under the body and uses drive shafts to each wheel. This ensures that the wheels have maximum contact to the surface in any situation and prevents the differential getting wedged in deep rutted tracks. The Prado has a rigid beam axle and each wheel cannot move independently for the best surface contact. The differential sits lower and is likely to get wedged(or damaged) in deep ruts.
The Montero has Engine Brake Assit Control(EDAC) which engages automatically when Low Range is engaged without a separate switch. This intevenes and automatically makes the vehicle crawl on steep descends by coordinating throttle and braking in conjunction with the Mitusubishi All Terrain Traction(MATT) controls. The Prado has Downhill Assist Control(DAC) which is a separate switch and does not work in conjuction with the driveline. It keeps the vehicle speed at 7km/h which is far to fast in most situations. DAC is just an elaborated handbrake.
The Montero comes with tiptronic gears as standard in all models. This enables the driver to manually select different gears in offroad situations to get the best gear(High Range & Low Range) for the job. The Prado does not come with tiptronic which gives less control to the driver.
So there are some points to note. Having said that, most Montero's in Sri Lanka have road tyres and never see more than speed bumps in car parks. This does not mean that the vehicles is not capable.