I think that the most common way to value Bitcoin is like valuing other currency by another currency.
Seeing to it that we all know all the factors that causes or affects supply and demand equilibrium.
Also the time we hold bitcoins. Time is very important factor.
As time passes by the value of bitcoin increases. So for me i value bitcoin like my own business that i need to monitor everyday to check if do i need to trade or invest to gain profit for it.