CLF is iron ore, WLT is coking coal. Both are highly dependent on blast furnace production of pig iron. Iron production is a function of economic activity, which is slow. BTU has a more diversified product range - PRB, Australian steam coal - and has significant sales to power plants in the US and Asia. This makes it financially more stable. Also, BTU is not as highly levered as the other two, i.e. balance sheet risk is less.