Summarize:

There are many different types of eyeliner that come in a pencil form, each of which has a different consistency and texture, application, and effect.  Powder-based pencils, sometimes called kohl, offer less intense color. They're also a good option if you want to smudge the eyeliner for a “smoky eye” effect. You can make the color appear more dramatic by wetting the tip before you apply the eyeliner. Gel- or cream-based pencils offer simple and excellent application. These pencils apply a rich and intense color. They're a good choice if you want to apply a winged, or cat eye, look. You can also purchase gel or cream eyeliners that come in a pot and can be applied with a tapered brush applicator. Liquid eyeliner pencils offer the most dramatic and intense application. Many liquid liners come in pen form (though it more closely resembles a felt marker), making application fairly simple. However, mistakes are very visible and difficult to correct because of the deep color, so you must have a steady hand during application. Tips range from very thin to thick depending on how intense you want the look or if you want to apply a cat-eye or winged look. Most companies offer different eyeliner formulas for different needs including sensitive eyes and organic, animal-friendly products. Some even offer formulas that include serums to elongate your lashes.  If your eyes are sensitive because you wear contact lenses, or if you suffer from allergic reactions to certain formulas, certain companies (like Almay) make non-allergenic (also called hypoallergenic) makeup, including eyeliner. If you prefer an eyeliner that is ethically produced, made of organic materials, and is not tested on animals, for example, companies including, Aveda, NARS, Arbonne, The Body Shop, and Josie Maran Cosmetics offer these products. Pencil eyeliners come in a broad range of colors from electric blue and emerald green to traditional colors like black and brown.  A good rule of thumb is to apply shades such as black, dark brown, deep plum, or grey if you want a more natural look. You can intensify or soften these colors as you like to achieve your desired look. Unusual colors such as electric blue, orange, or emerald green will really stand out against your eyes and eyelids, so it's a good idea to use them for special, non-professional occasions. If you want to tone down these colors for an everyday look, pair them with a darker, neutral-colored liner. Different eyeliner colors highlight each eye color differently. For example, plum eyeliner makes green eyes “pop,” while grey eyeliner looks great on blue eyes. Purple-toned liners can enhance brown eyes, and black is a good choice for any eye color. Once you've decided on the color, format, and formula, you are ready to purchase the pencil or pencils either at a store or online.  Eyeliners vary greatly in price. They can cost as little as 99 cents and as much as 50 dollars or more. You can buy eyeliners at retailers including drugstores such as CVS, stores like Target or Walmart, or department stores such as Macy's or Saks Fifth Avenue. Sephora, a large French makeup retailer with stores across the world, is another excellent place to purchase eyeliner. Most vendors, including CVS, Target, Macy's, and Sephora, also have websites where you can purchase your eyeliner. If you want to try out different colors or types of eyeliner, visit the makeup counter at your favorite retailer and ask about samples. They may provide you with samples to take home, or they may apply the eyeliner to your eyes so you can see how it looks.
Consider what type of pencil eyeliner to use. Consider the eyeliner formula. Choose an eyeliner color. Buy your eyeliner.