I agree Alon's method is an improvement. But as a financial trader I can tell you there is still an element missing. Many investments/trades have two variables that should be considered: the potential win versus potential loss (you do that), but also the chance on each of those happening. If you rate those equally (by not including them), you are back in the coin-flip realm.
I have therefore use your formula, but use a WEIGHTED potential profit vs weighted potential loss.