Gouache and watercolor are known to be two types of mediums that people normally use when they want to paint. There are some people who like gouache better and there are also some who prefer watercolor. The pigments of these two mediums are the same but the gouache is known to be more opaque.
It will come with a lot more pigment as compared to the watercolor. Some people prefer gouache if they want to have something that is more opaque. There is also a lesser chance that you will have granules on your artwork when you use a gouache. The gouache is also known to dry more quickly as compared to the watercolor.