Burr grinders are considered better, yet are slightly more expensive than blade grinders. Blade grinders work similarly to a food processor with blades that chop or slice up the beans. This can lead to dust being created during the grinding process and create a bitter coffee.
Burr grinders on the other hand use burrs which are abrasive surfaces that the coffee is ground between. Burr grinders give a more uniform grind and the best coffee grinders will have up to 18 different grind settings.