To poll or not to poll, is not a question.

A key can be read by either polling or interrupt. It all depends on the application. A beginner would think that an interrupt routine is easier to write. However, After being more experienced, you'll find that polling has many advantages over interrupt. For example,

1. Don't have to waste an interrupt pin, which could be more precious for detecting other events.
2. Some interrupt pins are fixed to falling edge detection. That prevents you finding out the state of key's up or down without using another pin.
3. When lots of keys are involved, wired-AND/OR them to the interrupt pin can be costly.
4. If ADC pin (by different voltage level) is used for keypad scan, interrupt has no use at all.

An exception is the rotary key scan.

Oliver