Some gel eyeliners aren't meant for the waterline. Anyway, I don't have a gel liner recommendation, really (that said, I've been using e.l.f.'s from their Studio line and think it's okay; I want to try Clinique's). But I do have a brush recommendation: Sonia Kashuk Bent Eyeliner brush. You can get it at Target. (Crown Brush, Inglot, e.l.f., and I think a few others also have them).