What I've heard of, the best 4x4 vehicle is a mercedes G-class. But very expensive to purchase and maintain, and not easy to get parts for in Africa, but very durable.
OKA's were pretty good too, and of course don't forget Unimogs. But I don't know how regular they break down.
@Towlersonsafari Did you deflate your tires? I Liuwa I've seen many selfdrives struggling in sand on 4 low, where they could drive pretty easily with half the tire pressure in 2wd.