Air resistance vs. free fall

In the absence of air resistance, it's easy - the ball comes back down at the same speed that it went up with. This follows from conservation of energy; the ball started with a certain amount of kinetic energy, traded the kinetic energy for potential energy as it climbed, and then reversed the trade and regained the kinetic energy on the way down.

In the presence of air resistance, the ball will come down at a slower speed and with less kinetic energy than it started with. The missing energy will have gone into friction with the air heating the ball and the air around it; the exact amount of energy lost will depend on many variables (the texture of the surface of the ball, the temperature and humidity, ....) and is generally hard to calculate.