Really depends if you want to get it all over and one with quickly or not. SAA will be the most direct, and out of one of the cities it is direct with no stops. FYI when you stop in Dakar you don't get to get off the plane so it make being on the plane close to 18 hours. Having a stop over in Europe is nice break but depending on your flights could mean a long trip. Contiental to SAA is an option. Plus then you can fly direct to CPT.

FYI- Star Alliance partners for the following trip would be UA, Continental, Lufthansa, SAA, and USAir (put I hear you should avoid them).

So I guess is do you want a long flight or 2 flights that are shorter. Also depends if your local has any direct flights to Europe. If so it could be quicker than going to another Washington or New York, or Atlanta (if you go delta which isn't *A).

Good luck with your decision and have a good time.