The best sensor to detect a ball is a "through beam" sensor. This generally requires an Emitter and a Receiver pair. When these two sensors are matched up, they look at each other, like the sensors at the bottom of your garage door. They don't care about the surface reflection of the part you are trying to detect.
A sample of through beam sensors can be seen here:
http://www.automationdirect.com/adc/...X-z-FE_Series)