I would recommend BP&W for most new divers today. This setup has been proven time and again to be better for attaining proper buoyancy and trim, as well as more streamlined for better propulsion. Most divers I have met eventually move to this platform at some point as they begin to dive more and move up in skill and confidence. The move from the stab jacket they were forced to buy to a decent back inflation system then requires some unlearning of being vertical in the water, finning to maintain depth, yanking on a hose to dump gas, and other bad habits reinforced in the OW course based on the limitations of the jacket. If the proper trim and technique were taught in the most optimal kit configuration from the beginning, the diver would not need to learn all this from scratch later (and often on his own without benefit of an instructor) when he upgrades to BP&W.
Now, that said, I do see 2 scenarios where I don’t recommend initial training in BP&W. First, if a new diver has no intention of ever buying his own kit and diving locally of carrying his own gear on trips, it makes sense to train on the type of BC that will be provided at rental locations. In the case of the "vacation only" tropical diver, this means a jacket from 1987 (OK, maybe 2002). The second case would be a diver with known back issues or other problems that have lead to the conclusion they will only dive sidemount. In this case, I believe they should learn OW in sidemount (not jacket and not BP&W), for the same reason - learn to dive in the config you intend to use long term.