Although the US$ used to be king, I've never had a problem with euros in the the CFA franc countries (whether XOF for west African countries like Benin, Burkina Faso, Mali, Senegal or XAF in countries like Cameroon, Chad, Gabon or Equatorial Guinea). Morocco definitely prefers euros. The advantage of euros in these countries is that the French treasury guarantees the exchange rate with the euro (though with all the problems of that currency right now it may not be so good in the future).