Gender Studies is a subject which is about woman and gender issues. GS also have thoughts in Human Rights and other things like that. GS is an interesting subject.
Whereas ES is more science and less an art. So choose ES only if choose geography.
I think that syllabus and toughness of subject do not matter soo much. The thing that matter is your own interest.
I have my subject choice as following
International Relations
History of USA
Philosophy
Psychology
Gender Studies