So I decided to swatch all my black eyeliners (pencil) and see which one of them is the blackest and most smudge-proof.
1)MAC Kohl power eye pencil in Feline ($16)
2)Maybelline Colossal Kajal in Black ($8)
3)NYX Slide on Glide on eyeliner in Jet Black ($8)
4)Urban Decay 24/7 eyeliner in Zero ($19)
From Left to Right: MAC Feline, Maybelline Colossal Kajal, NYX Slide on Glide on pencil in Jet Black, Urban Decay 24/7 in Zero
I wanna say MAC Feline and Maybelline Colossal Kajal are pretty similar as in they are both rich, sort of glossy blacks. NYX Slide on Glide on pencil is very similar in texture to the Urban Decay 24/7 pencil. I don't own the Urban Decay 24/7 in Perversion which is even blacker than the original Zero.
To sum it up, MAC Feline is the blackest of them all and NYX Slide on Glide on pencil held up best in the smudge test. My favorite at the moment however is the Maybelline Colossal Kajal as it is a rich black and smudge proof upto 6 hours (as it says on the packaging). However, MAC Feline being a non-waterproof eye kohl delivers the most sultry, smokey, smudgey eyeliner look (if thats what you are going for). If you apply an eyehshadow primer before using MAC Feline and set it with some translucent powder and re-apply throughout the day, it actually works pretty well.