One thing that you should know about me is that I rarely leave my house without eyeliner on. For this reason, I am always on the lookout for potential new eyeliners that will not budge.
Since I have oily eyelids I find that even the toughest eyeliner sometimes smudges, especially if I use them on my waterline or on my lower lash line without some sort of base or eyeshadow or primer.
I have tried a couple of gel liners but I think from the ones I have tried I found that the Essence Gel Liner in 01 'Midnight in Paris' is the one I like best, considering the price it costs (not so sure but I think it was around 3 Euros).
The liner comes in a small glass container and you get 3grms of product. Unlike some other gel liners, this does not come with its own brush (but Essence do have a small angled eyeliner brush with very soft bristles). This eyeliner goes on really smooth and once dry, stays on for hours. It is highly pigmented too so there's no need to go over and over again till you achieve the perfect line and colour (I'm so sorry but I forgot to swatch it!)
I would recommend this for a) its price b) its longevity c) the colour payoff