Always BPA. It can be a tie-breaker at the top. But, considering almost all players drafted aren't going to make a serious impact for 3 years (and projecting your needs 3 years down the line is nearly impossible), you always go BPA.
Take Carolina in the 2014 draft where they took Fleury. They felt they needed a defender because they were very weak at the back, passing on Ehlers and Nylander, but they had both Staal brothers up the middle and Skinner on the wing. All of sudden Pesce and Slavin emerge as legit players, and they end up drafting the next year in a spot where the consensus BPA is a defender. Now, they have a bunch of defenders, traded Eric Staal as he was an upcoming UFA, and lack forward depth.
Take Carolina in the 2014 draft where they took Fleury. They felt they needed a defender because they were very weak at the back, passing on Ehlers and Nylander, but they had both Staal brothers up the middle and Skinner on the wing. All of sudden Pesce and Slavin emerge as legit players, and they end up drafting the next year in a spot where the consensus BPA is a defender. Now, they have a bunch of defenders, traded Eric Staal as he was an upcoming UFA, and lack forward depth.