When traveling and working in South Africa, I've always used Newman's guide to the birds of Southern Africa, and more recently, I found the Sasol guide to be helpful as well. (I discuss both briefly here.) Now, I've got on my desk a copy of Princeton's Birds of Southern Africa: Fourth Edition by Ian Sinclair, Phil Hockey, Warwick Tarboton and Peter Ryan. You will know Sinclair from his South of the Saraha bird guide.
All three books cover about the same species, as far as I can tell (just under 1,000) and have a similar range of illustration and information. They all have overview graphics that help narrow down the species, and other helpful information.
There are things I like about the new Sinclair book that you might appreciate as well. First, the range maps are more detailed and updated, and probably the most accurate of any in a current field guide. Sasol has helpful inflight graphics arranged to group several similar species together, but Sinclair has the in flight images in the same place as the other images of each species. That might make Sasol better for the novice who needs to narrow down "hawk thingie" to a more fine detail, while Sinclair would be more useful to the pro. (Sorry, I'm not making the comparison to Newman right now because I can't lay my hands on my volume right now. Might have left it at Lynne's house. In Pretoria.)
Obviously, you need more than one field guide, especially if you are traveling with more than one person. (Always bring different guides, not copies of the same, where possible!) and at the moment I'd suggest the new Birds of Southern Africa: Fourth Edition because it is the most up to date, along with the Sasol.