There is no as such hard and fast rule that a particular type
of inventory valuation may produce more net income. It totally
depends upon the inflation that is price of the raw materials.
In case of inflation, when prices of the raw material are
increasing, FIFO method will give more profit than other other two
methods.
In case of deflation, when prices of raw material are falling,
LIFO method will give more profit than other two methods of valuing
inventory.
If there is no change in the prices of the inventory than all 3
methods would give same level of profit.