My experiences in Australia are now 20 years old, and since that time, a lot of 4x4s have entered the marketplace. Most of them, however, are not built for serious terrain. They've replaced the station wagon as the family people-hauler and are designed more with luxury and amenities in mind than competence over rough ground.
A good friend in England uses a diesel Land Rover Discovery for the English countryside and it's rugged and dependable. I've driven it over there and it's as competent as a Rocky Mountain trail horse. He has a Range Rover, too, which is also capable, but a lot nicer and more expensive, and not available in stick shift. Shifting is more work, and a lot of Americans don't want to be bothered with it, but in remote areas, the ability to start a vehicle with a weak battery by pushing and popping the clutch can be quite handy.
Unfortunately, diesel Land Rovers are not readily available in the U.S., if you were planning to buy here, and a late-model Range Rover is probably more vehicle than you need.
This brings us to Toyota 4x4s. Toyota has an excellent dependability reputation and mechanics in many parts of the world have seen and worked on them. While the Land Cruiser was a trail standard, it is now much more luxury-oriented than the old ones. They're as expensive as luxury sedans and probably, like the Range Rover, more vehicle than you need or want.
My wife and I almost bought an '89 Toyota 4Runner, used, in 1996. That older style was smaller, lighter, nimbler in a tight spot than the bigger, heavier, wider ones that appeared during the SUV craze. There are some clips on YouTube of people driving in Sierra Leone, and I see 4Runners passing by. I'd start there. Test drive a range of years, to see how the feel and appointments change, and what you like. A low-mileage, rust-free example that has been well-maintained would be a good starting point.
An older one that is in excellent shape may serve you well. Older vehicles are simpler, which means they're easier to understand and troubleshoot. Lots of old vehicles appear to be on the roads in Sierra Leone, so a mechanic is as likely to have seen an old one as a new one - probably more likely.
