Final answer:
Among the ECOWAS member countries listed, Sierra Leone has faced significant economic challenges in recent years, implying it may not have experienced the same level of economic improvement as others like Ghana and Ivory Coast.
Step-by-step explanation:
The Economic Community of West African States (ECOWAS) was established to foster economic integration among its member countries. While some member states have seen improvements in their economies, others have not experienced the same level of growth. According to the information provided and current economic data, the country among those listed that seems to have faced more challenges in recent years would be Sierra Leone. Although not explicitly stated in the provided reference material, Sierra Leone has had a tumultuous economic history, impacted by civil war and the recent Ebola crisis. Meanwhile, countries like Ghana and Ivory Coast are highlighted as bright spots with growing economies.
As for Nigeria, despite having the largest economy in Africa, it faces significant challenges such as inflation and insecurity, which can impede steady economic growth. Yet, it's not indicated in the reference whether Nigeria's economy is improving or worsening. More research would be required to determine Nigeria's current ECOWAS economic standing relative to the other options provided.