In all pressing movements for bodybuilding purposes, you want to grip so your forearm is straight vertical when your upper arm is parallel to the floor. This will be the best grip to place emphasis on pecs for chest movements or delts for military. You'll see that this results in a pretty wide grip. The closer grip you use, the less delt & more tricep is used.
If strength training, then you'd use a slightly closer grip that would allow you to use heavier loads.