There is no magic 'best' exercise. I remember reading a study someone posted that decline with dumbbells recruits the most muscle fibers, but as far as developing your chest I think there would be a bigger emphasis on your nutrition and how you lift versus what specific exercise you do. For example I feel I could develop a better chest by simply doing push ups compared to some of these clowns that bench regularly at the gym because they neglect the more important variables in body building.