Is ease of use a priority? If you simply want to make a fresh cup of coffee without the hassle of a lot of cleanup, a blade grinder is the way to go, and many users say they work very well for a drip coffee maker.
Do you just need a grinder for spices or seeds? In that case, don't spend the big bucks. A $20 blade grinder works very well for these items. Some grinders can also handle nuts, but you may be better off using a good food processor for that.
Are you a coffee connoisseur? Burr grinders crush beans slowly, which preserves flavor and aroma -- so if you're looking for the best possible taste and fragrance, go with a ceramic burr coffee grinder. This is particularly important if you drink espresso, which is one of the most challenging grinds.
Do you want doser or doserless? A doser is chamber that is separated into sections. The sections rotate so that each one can be filled with a single dose of ground coffee, which makes it possible to grind, hold and dispense enough grounds for several cups of espresso in quick succession. Most coffee aficionados prefer doserless because they don't like the idea of the beans sitting in the machine and perhaps getting stale. Doserless machines are also easier to clean.
Stepped or stepless? Stepless grinders do not have presets, rather they have an infinite number of grind settings. They are not as easy to use as stepped grinders, but true connoisseurs love them for the fact that they completely control the grind.
Researching coffee grinders can be daunting for the average person. Sites where passionate coffee aficionados gather can be quite strident in their opinions, and quite contemptuous of anything they don't consider a "serious" grinder. Some of these folks have such sensitive palates that they're rarely pleased unless they have a professional barista-quality brew.
We'd like to say this: Don't be intimidated. If you have a standard drip coffee maker you'll probably be perfectly satisfied with a blade or less-expensive burr grinder. Even these, reviewers say, raise the taste level of a cup -- or pot -- of coffee without the need for a several-hundred-dollar grinder. In fact, unless you have a super picky palate, one of those less-expensive grinders will be fine for most specialty coffees, and work especially well for pour-overs. If nothing else, start small and work your way up to more expensive options as you become more knowledgeable and experienced in the art of coffee grinding.