The return speed will be slower than its initial speed.
Work Step by Step
When air resistance cannot be neglected, on the way up the ball loses more speed each second than if there were no air, and does not rise as far. On the way straight down, air resistance decreases the magnitude of the acceleration and the ball gains less speed each second than if there were no air. The conclusion is that in the presence of air resistance, a ball thrown straight upward returns to its starting point moving more slowly than its initial speed.