Looking at new. I would also be inclined to agree about Toyota (which I have experience with and currently have a 78) although I have never driven a G wagon. I know from experience that Toyota parts are generally not an issue in most of Africa (most NGOs etc are using them everywhere), and I believe Mercedes Benz have a similarly good Africa network (although perhaps not AS good). For Africa trips, I am carrying most parts anyway, and am yet to have a mission critical scenario of being unable to get parts locally. The differences between the two options may well be small enough to render it a question of simply personal preference...What age of vehicle? Both are immensely capable and rugged. Parts <should> be available for both in most if not all African countries. Personally I would give the reliability nod to Toyota, but if you’re buying used, it’s a crap shoot.
Looking at new. I would also be inclined to agree about Toyota (which I have experience with and currently have a 78) although I have never driven a G wagon. I know from experience that Toyota parts are generally not an issue in most of Africa (most NGOs etc are using them everywhere), and I believe Mercedes Benz have a similarly good Africa network (although perhaps not AS good). For Africa trips, I am carrying most parts anyway, and am yet to have a mission critical scenario of being unable to get parts locally. The differences between the two options may well be small enough to render it a question of simply personal preference...
Located in UT but the vehicle will remain based and registered in Europe (I decided to not get into the problems relating to importing such a vehicle new to the US....) Yes, those things could cause a major a problem in Africa, giving Toyota a significant edge - accepted.Where are you located? Are you talking a new USA G-Wagen (ie G550 or G63), or a new Euro G-Wagen (G 350D), like the Professional line?
Regardless, personally I wouldn't feel comfortable taking either across Africa; too much German overcomplication with too many sensors and electronic widgets to be problematic, you'd need to purchase($$) and carry a factory Xentry/DAS Mercedes scan tool, etc.
I'd feel much safer with the Toyota, even if it is like driving an appliance. My $0.01.
There's a lot of different versions of the G. You didn't say if it was new or even if it was the diesel or the G550/G63.
If it is the newer G550/G63 models, know that they take Premium Grade gas. If you're going cross-continent, I wouldn't expect a lot of stations to have that.