Without a doubt the Remington. Although no 416's are what I would call popular there anyplace. The majority of PH's and locals use a 30/06-375HH-458 win mag or some of the various 9.3mm cartridges. In reality only the Americans coming over bring the 416 rem mag to hunt with.
I think this is true of South Africa, since it is clearly the most budget-oriented destination, both for the client and the PH.
But Africa is a large continent and in other countries there are quite a few 416 Rigbys, especially where the 416 rem is disfavored due to pressure problems in the past, feeding problems with the model 70, and extractor problems with the model 700.