I agree with moving this to training board.
Best chest exercise may depend on the individual.
Guys who have a protruding sternum are more anatomically built for pressing. You'll see guys who have a breast plate that looks like the bottom of a boat. These guys have a tremendous advantage for benching because the pecs are more involved. Since their pecs are more involved, they also grow more from this type of exercise; their is a greater muscular ROM, more pectoral involvement, and more pectoral stimulation. These guys are just built for benching.
Dumbells have a few advantages:
greater stretch
greater muscular range of motion
For guys with a narrower breastplate, the difference in the muscular range of motion for db's may be more significant. This is because the flat-breastplated-lifter, in comparison to the barrel-chested lifter, gets much less pec involvement with a bench press, but with a db press, he gets only a little less ROM compared to the barrel chested lifter.
For your barrel-chested lifter, the concentration and balance required to perform DB presses may take away from the ability to exert sheer force, making BB benches the better choice.