Answer
The softball.
Work Step by Step
The solid softball has most of its mass closer to a rotational axis passing through its center and has the least rotational inertia relative to its own mass. It will have a greater acceleration than the hollow basketball, and wins the race.
By this reasoning, one may conclude (and verify experimentally) that a solid sphere of any mass and size beats a solid cylinder of any mass and size, which in turn beats a hollow ball of any mass and size.
This is discussed on page 138.
