The best type of mill for grinding coffee is made with burrs. Mills for home use have conical burrs that turn, and a stationary conical plate. Commercial mills usually have plate burrs that are fed from a hole in the center, and grind against a stationary plate.
You can adjust the distance between the burr opening to produce your preferred coarseness of grounds. This is important to get consistent results from every brew. Both electric and manual mills will give you similar results; the manual ones take more time and a bit of energy.
Manual mills with conical burrs grind more slowly and thus won't overheat the grounds from the friction. Overheating from continuous milling on fast, electric mills causes the volatile oils to dissipate faster, thus altering the taste of your coffee.
Manual coffee mills work well from espresso to automatic drip, however they tend to produce uneven coarse grinds, as might be used for percolators. Mills with hardened steel or ceramic burrs also tend to perform well in grinding Turkish coffee.
For most automatic drip coffeemakers with paper filters, and for others where there is leeway in the fineness of the required grinds, such as with the French Press, the popular and inexpensive bladed grinders can prove to be adequate. To get a more even grind, shake the unit as it's grinding, so that more of the coarse pieces of beans will come in contact with the blade. Just don't grind it to a powder.
Because it's not too easy to totally clean out the taste of coffee and spices from most coffee mills, we recommend using them only for coffee. For spices, we recommend a small, versatile, easy to clean food processor, or an appropriate pepper or salt mill with ease-of-cleaning features.
How Coarse/Fine to Grind
An espresso maker uses very fine grounds, a percolator uses very coarse, and an automatic drip somewhere in between. And they won't work properly, or make good coffee, if the grounds are not the appropriate coarseness.
Get a sample of store-bought ground coffee to help you determine how coarse or fine the coffee beans should be ground for use in your coffeemaker.
Test your coffeemaker to make sure the coarseness is acceptable, and save a sample of the ground coffee for future reference.