I have a bunch of different brand black eyeliners so I thought I would compare them for you guys.
Fom left to right: MAC smolder, Urban Decay zero, Sephora, Milani black, MUFE 10, Clinique really black, Este Lauder soft smudge black, Cover girl black onyx, MAC black funk, (and not pictured until last picture) Avon blackest black
Each liner had good pigmentation but some swatch more easily then others. The easiest to swatch were MAC black funk, MAC smolder, and Covergirl black onyx. Those three eyeliners were very soft and very black. These would be great to use on the upper lash line or lower lash line.
Best liners for waterline: Urban decay zero, and MUFE 10 These liners are waterproof and will stay on your waterline the longest. I personally hate it when an eyeliner runs our of the outer corner of my eye. For me the sephora liner and the two mac liners ran the worst for me on my waterline.
Best smudge: The este lauder soft smudge black was the easiest to smudge because it was made to do it. This liner would be great for a smudgy smokey eye look on the top or the bottom lash line.