There are two types of eyeliners that I think should belong in every kit. The first, a smudgeproof (or waterproof) one that provides definition and makes the eyes really stand out. The other, a khol eyeliner - this type, you can smudge and is essential if you want to achieve a natural look.
I'm a fan of Prestige Cosmetics' Classic Khol Eyeliner because of the variety of colors available, the quality and affordability.
The eyeliner's firmness is just right for a khol pencil. It's soft enough that it doesn't tug your eyelid nor does it feel scratchy. But it's firm enough that it won't break with the lightest touch.
For contact lens users, this isn't irritating at all. I've used it with and without lenses and it felt comfortable. One should note, however, that this isn't waterproof so you wouldn't want to use this on your waterline unless you're going for the panda look.
left to right: Black Brown, White, Wine & Black
To get a soft-focus look, take an eyeliner brush and fill the space in between your eyelashes. Or you can skip the brush and apply it directly using the pencil - the line may look thicker this way so a bit of practice is necessary. The result is a subtle, everyday look. It's great for those who want to make their eyes appear larger.
When I'm too lazy to wear more than one eyeshadow, I take this and shade the outer corners of my eyes. I then take a bullet brush to blend it in and soften the look. The result? A soft smokey eye.
I've been hooked for several years now and simply cannot go without this product. What's your favorite type of eyeliner?