Time. If you have done N/A, do S/A or Africa, but not both. You are only giving yourself 2-4 days each place, why spend a day or two of it flying around? I haven't been to Africa much, so I can't give an opinion. (though who said that opinions are like *******s...everyone has one? Blakey or someone? can't remember) South America is worth the trip, though. Easter Island and all of Peru I enjoyed. Brazil and Buenos Aires are always high on people's lists.