Gel and cream eyeliners are different mostly in formula. Studies show that cream liners are used more often than gel liners, however, gel liners better suit beginners. When one uses a cream eyeliner, the eyes may have a natural, silky smooth look. Unlike cream liners, gel eyeliners give the eyes a smoky look. The gel liners are very easy to apply on the lash line using a small brush. Cream eyeliner is smooth and soft whereas gel eyeliners are not as smooth and soft to apply. Unlike cream liners, gel eyeliners usually stay on longer. A lot of cream eyeliners are composed of creamy substances and come in a tube or pencil form whereas gel liners usually come in a jar or pot. These are just some of the differences between the two, but I can honestly say that I love both gel and cream liners. Especially those by Smashbox brand.
Hope this helps!