I'm assuming this question implies that the surface area is in relation to the volume of the pieces. In that case, the SMALLER the size of each piece, the larger the surface area. This is because more particles are able to fit into the container if they are smaller, leading to more surface area. Since more pieces can fit into the container, MORE collisions happen according to collision theory. I cannot add a link, but for a helpful analogy, look up "How To Speed Up Chemical Reactions (and get a date) - Aaron Sams.
