Welcome! You have found the correct resource for G information.
The engine choice depends on your desired use. If you need to drive mostly on the highway, the V8 will drink a lot of fuel, but will be happy at high speeds. The 300GD with the 5-cylinder OM617 engine, 5-cylinder OM602, or 6-cylinder OM603 engines will have limited power and top-speed, but are ideal for off-road driving and rely on only the most basic electrical and mechanical systems possible. They are more field-serviceable, and slightly more fuel efficient. The one, rare model G300DT has the OM606 turbo diesel engine, and is very capable on both the freeway and off-road. It does rely on electronics though.
Parts are available mostly in Europe, but many bearings and seals can be found in local industrial supply houses. In the US, certain versions of the G-class are sold here, so the parts availability for those models is good.
Best of luck with your search!
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