I have a pet peeve with eye-liner that smears, which is almost impossible to control, so your two choices are to carry Q-tips with you, or use a smudge-free liner which won't budge and give you a fresh look all day.
Disadvantage: If for some reason you are lining your eyes, and it's not completely straight, smudge-proof/waterproof liners will usually dry quickly and be difficult to take off.
Advantage: A smudge-proof liner plays a massive role when you are trying to obtain your signature "cat-eye" look. By lining just the outside of your eye, you can secure that it will not smear all day.
The "cat-eye" is a personal favorite of mine, partially because my eyes are almond shaped and it gives a distinct appeal with or without any shadow, and you can play with different colors.
Rihanna's make-up style is admirable, and I have yet to find out her artist, but she's a fan of the "cat eye" and utilizes it with a range of different colors for her eyes and lips.