If you debounce in software, you should think about an integrating algorithm rather than a simple timed debounce.
I found that response time was too long when I relied on a simple debounce algorithm, which is why I reverted to analog. (I originally went analog because my first microcontroller was a Basic Stamp, which had something like 20 bytes of RAM.)
An RC debounce can effectively discriminate between a momentary loss of contact due to dirty track, versus when the last little bit of wheel has left the sensor rail. An integrating algorithm can emulate that effect.
