They accelerate downward at the same rate, but one WILL eventually fall faster than the other. For example, both will fall at 9.8 meters per second until they reach terminal velocity. I tend to think a baseball will fall faster that a softball because it's about the same weight as a softball but it's smaller, so its more aerodynamic. Google 'terminal velocity'.
If there was no friction (wind resistance) they would fall at exactly the same rate. In the real world there is friction that is not exactly true. I would bet on the softball to fall just slightly faster because it has a smaller cross-sectional-area-to-mass ratio.