Equity Valuation: Sum-of-parts, PE, PB valuations?

There are no specifics as to when one method is preferred over another and indeed each simply suggests one aspect of what the future value may be. The DCF and DDM simply establishes an upper bound on what the value to an investor may be by comparison to a synthetic investment at the discount rate chosen. Using an industry PE or PB ratio simply determines what the general trend may be on the assumption that the intrinsic PE and PB tends to be determined by the business model which is common in an industry sector hence any deviation from the industry average is the extrinsic or speculative component which should average out, basically they try to determine what value it should be gravitating towards by virtue of estimated earnings for the PE ratio and by virtue of the company's resources by PB ratio. It's like those hurricane tracking forecasts, they have several models for the forecasts and if they all say the same thing then you have a higher degree of confidence in the forecast. The same is true with financial forecasts, the only appropriate answer to your question is that you always use all of the methods.