Apart from the use of $2 per day measure of poverty line as adopted by the World Bank and other development multinationals, other measures may be more appropriate for poverty measurement in sub-Saharan Africa.
the appropriate indicator depends of course on the topic you want to adress. As a rule of thumb, I'd always prefer the Human Development Index as poverty indicator. It is based on sound ethical theory (Sen's capability approach) and there is ample of literatur and data available. Last not least: you can compose your own indicator , if needed.
I think that considering the poverty line as $2 per day is not appropriate for sub-Saharan African, even in several countries. The prices and the purchasing power is different from one region to another especially for sub-Saharan African compared to other regions. I thing the best methods for analyzing poverty is to calculate a local poverty line taking into account alimentary and non-alimentary expenditure.