All things equal: standing on the glove side of the rubber is a slightly shorter, more direct line to the plate; standing on the throwing arm side of the rubber is a slightly longer, more angled line to the plate.
Experiment with both. How old are you? My son is 13 and has settled (for now) on the throwing arm side of the rubber. Over the years, however, my son switched from one side to the other a few times, such as when he struggled with control. The change would give him a psychological benefit, and it would pay off with better control!