I love a felt tip liner for quick and easy liner application and this one from Soap and Glory has been my faithful friend for years now. There are a bunch of great options on the highstreet now but not all are made equal.
Soap and Glory's Supercat Eyeliner is a gorgeously pigmented formula. It's very black and dries to a semi matt finish - it's not glossy but it isn't matte either, which I personally really like. It lasts well on me and though it will wash away a little at the wing if I'm tearing up it does a far better job than some other felt tip liners I've tried.
What I really love about the formula though is that it's quite wet. It doesn't bleed and it's easy to use but there is always plenty of product on the applicator. For this reason it applies monthly and seems to last absolutely ages! It's also buildable (not that you need to build it) in the sense that if you're thickening your line you can apply on top of previous strokes and it won't disrupt the liner as some similar products will.
There's nothing too special about the felt tip but it's a nice length and thickness making it very easy to apply. I also like that the lid has a nice click stopping the product from drying out.
I've tried plenty of others but I always come back to this for it's pigmented and smooth formula. At only £6 this is a massive bargain.