Answer
It returns at a slower speed.
Work Step by Step
When the baseball is on the way up, the force of air resistance does negative work on the baseball (force down, displacement up). When the baseball is on the way down, the force of air resistance again does negative work on the baseball (force up, displacement down). Gravity does zero net work on the round trip, so the net work done is negative.
The net work is the change in kinetic energy, so there is less kinetic energy at the end than at the beginning, i.e., it returns at a slower speed than it started with.
