Think of GRE as an aptitude test, and TOEFL/IELTS as a language test. There are a few universities that have completely waived off GRE, some universities keep GRE optional(in that case better submit a GRE score, as most other students would do and get an edge over there), and some keep GRE mandatory. So I would highly suggest you to take the GRE. Out of TOEFL and IELTS, you need to take one. Depending on the country, you can chose one of them, for example in US, TOEFL and IELTS both work, however TOEFL is preferred by some top universities, for Canada, UK, Australia, IELTS is preferrred.
I have given GRE and TOEFL, and scored 316/340 and 105/120 respectively.