Cash is better because you can easily use it to buy your needs anywhere in the country/world. You pay cash when you buy street foods, for your children's allowance, to pay for public transportations. People also are accustomed in using cash in majority of their transactions.
Bitcoin is much better to use because it's much easier to send to the people in Africa and other parts of the world without having to go out to a bank.
It's easier to send funds globally and not just the people of Africa so far as there are exchanges where you can withdraw them unlike fiat/ cash payment processors like paypal or western union and moneygram which have certain jurisdictional restrictions and huge transaction fees.