James and Woodsman are spot on, get a Jeep YJ or a TJ. Build it up if you want to but try it stock (or near-stock, ditch any non-AT/MT tires) first, you might be surprised what it's capable of, driven properly... I would consider the YJ to be a general purpose (yes, I know Jeep=GP isn't the origin) scout car that's good for most practical off-roading - actually trying to get places, not seeing how big of a rock you can crawl - without much modification. If you want a built one bear in mind that as soon as you change one thing, you will need to change a whole bunch of other stuff to compensate (bigger tires require re-gearing, for instance).
Don't mind RYP, he was probably bitten by one as a kid or something. OK, Landies are great. But most parts of the world seem to have a preponderance of one or the other... Go for whichever has more of a local following, as a specialist mechanic, club or parts source will be invaluable. In Taiwan (which is home to some of the world's nastiest annual typhoons, flooding and landslides, and is maybe 65% mountainous jungle) there'll be a Jeep garage and club in every county, but I think I've seen fewer than a half-dozen Landie Defenders in 5 years. Lots of luck getting parts.
Don't get a Jeep if you want a smooth ride. You'll feel the bump driving over a shadow.
Top Gear's South America special is a blast: tatty Range Rover vs. ragged-arsed Land Cruiser vs some sort of Suzuki thing.http://www.streetfire.net/video/top-gear-bolivia-special-season-14-episode-6_1994638.htm