Both methods give you the same valuation for the investment if they're under the same assumptions. Thus, the choice is mostly a matter of convenience. As a general rule, the WACC method is the easiest to use when the business maintains a fixed debt-to-equity ratio over the life of the investment. But if the company adjusts its debt every year according to a fixed schedule known in advance, the APV method is better because you will need to calculate a different WACC for each year.