I was never satisfied with the brushes I've tried for my gel eyeliners. So when you are never satisfied, you keep on searching and trying out different ones. I have tried probably 9 or 10 different brushes. I still own them and use them. I have thin, flat, pointy, all sorts of eyeliner brushes from bobbi brown, napoleon perdis, sigma, MAC, maybelline, etc..... Heck I even tried lip and concealer brushes as eyeliner brushes. None of them seem to make dark consistent lines that are precise.
Until..... I met Smashbox #21 Arched Eyeliner Brush ($20).
I believe this is a vegan friendly synthetic brush (if it's important to you)... it has the same head as the Smashbox #8 Brush, but has the bend. The bend makes it a lot easier to get into the inner corners of your eyes without having to covering your view with your own hand. The tip picks up the right amount of gel liner and you can rim your waterline with precision.
Here are some comparisons of the brushes I had in my makeup bag. You can see that the Smashbox brush is much thinner than the other two.
Here are some lines I created with the three brushes above. Sorry the order goes in reverse. (ooops @.@)
First one is from the Myglam Concealer Brush, the second, Sigma E05 Eyeliner Brush, and the last three are lines I created with Smashbox #21 Brush with just one dip into the gel liner. You can see that they come out a lot darker and precise than the other two while being able to create different types of lines.
This brush is definitely getting Holy Grail Status!!! I looked at my eyes (especially my lower waterline) and I was so satisfied with the precise perfect clean lines it created. Only thing I will mention about the Smashbox brushes is that after awhile, it needs to be replaced... (probably faster than some of my oldest brushes) It maybe the synthetic brush factor, but I can see this happening with this brush as well. Probably not within a year, but even so, the size and everything else is so perfect that I'd repurchase this brush. :)
You can get yours at, Sephora, Smashbox.com, Nordstrom, and Ulta.