Normally (before coronavirus), the top universities do like students to have GMAT or GRE, it can help with admissions, and it also help with scholarships.
You also can take their entrance test, but if you are applying to many universities its better to have GMAT or GRE, so you don’t have to take the entrance test for each university.
GMAT is only for business schools, its a bit more focused on math and generally a bit easier if you are stronger at maths and not native english speaker.
GRE is accepted by many universities for graduate programs, normally you would get higher score if you are better at english and weak at maths.
Right now, due to the coronavirus, you can apply to the top universities, and take their entrance test, or GMAT or GRE at a later date. Currently GRE and GMAT do have online option.