It also sounds to me as if *A will fit you better than the others.

Program:

A) If you're doing mostly to-from west Africa without a lot of internal flights then it sounds like UA Mileage Plus is the winner. Pretty good at crediting full miles on most fares of carriers relevant to your trips, reasonably good award chart, very easy to cash in awards on most *A partners online, no fuel surcharge on award tickets, free UA E+ seating on UA metal if you make Gold or better (well, Silver but day of travel only).

B) If you have a lot of regional flights in west Africa, there isn't much as far as actual *A goes, maybe a couple of 5th freedom routes here and there. But there is ASky, based in Lome but with lots of regional routes that are point to point, don't have to connect in Togo necessarily. They are a subsidiary of ET and part of ET's Sheba Miles program. If you search around there are a few reports of their program and it seems solid, reasonable earn on most *A carriers, decent award chart, easy redemption on ET flights. Hopefully Asky (KP) will eventually be brought into *A as a full or regional member, it's been rumored since ET's joining but hasn't happened yet.

Carriers to/from the US for West Africa:
- I don't see TK, ET, MS, or SA as being terribly convenient for connections to west Africa unless the timing is just right and you would have otherwise had a terribly long layover somewhere else.
- SN has an extensive network to Africa and I believe covers every country you need to go to. They are marketing themselves as ideal for US to West Africa, so I assume they have the flights timed well in BRU but haven't looked myself.
- LH as mentioned already hits several points in West Africa

For South Africa, probably SA makes the most sense as long as you can buy a full mileage earning fare class as you'll save a lot of time avoiding the connection in Europe.

For South America, UA, CM, and AV will get you around where you need to go quite well.