From Michael Moretto, and published at Seeking Alpha, this guide goes through some of the factors that make a certain gold company a better pick than others. First is size and production, with large mines being evaluated as better than small ones. Second is juridisction: the better companies have mines in low-risk jurisdictions. Thirdly is grade: at a minimum, an open-pit mine should have 0.8 g/t; an underground mine, 4-5 g/t or better. Fourthly is byproducts. Gold companies that aren't pure plays tend to be rated less highly than those that are.
It's a useful guide for beginners, but the market has a way of discounting these factors. Suffice it to say, though, that a gold company that appears 'cheap' from a strict quantitative comparison often has some wrinkle in its deposit(s) that make it a false bargain.