I have heard that decline dumbell press targets the most of the chest followed by decline barbell press as according too some form of scientific study that noted the number of muscle fibers used for several chest exercises. But today, while scanning the book: Strength Training anatomy by Frederic Delavier, it is flat bench targets the largest portion of the chest and barbell and dumbell are much more similar in isolating this area than you may think. so classic bench press IS the king of chest exercises after all! I have recently re-enlisted it as my main chest builder and starting exercise (replacing 15 degree incline dumbell presses) and I can already tell that i am in for some serious growth!!