Which is the best principal of finished goods stock valuation?

FIFO= first in first out,, that is the best principal

FIFO, LIFO, W(AVG) these all are the method of maintaining stock. But asking here about valuation of stock goods. It should be calculated on cost of goods sold per unit basis. 

FIFO. Not only finished goods stocks can be evaluated, but also the finished goods that arrived first.

There are a number of ways of determining the cost of a stock item depends on nature & type of stock.

Stock may be valued on a 'first-in first-out' or average cost basis or a reasonable approximation of these.