When talking about unmodified, out of the box 4x4's meant for tough conditions and professional use, my money is on the Mercedes/Puch G-class (work variants that is, not so much the bling versions). As a working vehicle, the G-class' off-road and other field capabilities are really second to none. Its overall technical quality and durability are also very impressive and contribute to the supreme overall usability.
1983 Mercedes G-Klasse 300gd With more than 650,000 miles on it - this car has worked hard for Merv since he bought it when it was 6months old. It was bought because at that time it was the only car that size that would pull any broken down trucks of his off the motorway fully freighted!