Well, good question but I think it is the sum of exercise that builds chest. The chest is a large area-there are many layers of muscles that make it up but it has three main strands of muscle-upper chest, mid and lower chest that adjoin together. The focus I think would still be on bench. Although it is a compound movement it being a large muscle group is more apt to respond to more trauma the mass exertion of the exercise puts on it. I think to build a chest you should start with bench. Then when you see a response you use butter fly or upper chest, dips and lower chest exercises to fill in the blank areas. If you want a bigger upper chest you do more incline movements, if this is good and you want more striation or definition in the middle you focus on butterfly as a first exercise. The best thing I think you can do is focus on the weak muscle. I myself have a relatively low bench but I am satisfied with my chest mass so it does not bother me. I was lacking on upper chest so I made it the focal point of my routine for a while.