From the point of view of a financial analyst, when evaluating companies that use different inventory cost assumptions, in a period of:

The most useful estimates of inventory and cost of sales are those that best approximate current cost. Whether prices are increasing or decreasing, FIFO provides a better estimate of inventory values, and LIFO provides a better estimate of cost of sales. If prices are stable, there is no difference between LIFO and FIFO estimates of inventory or cost of sales.