1. What is your strong suit? Quant or verbal? The quant section on the GRE is significantly easier than the quant section on the GMAT. But the GRE verbal section is extremely challenging even for native English speakers. So if you are weaker in quant, you might be better off taking the GRE. Whereas if you struggle with verbal, the GMAT may suit you best.
2. How well do you expect to perform? A key factor that determines a business school rating is the average GMAT score for its incoming students. The GRE, on the other hand, is not used for ranking purposes. So even if you are a strong candidate, a below-average GMAT score may deter schools from accepting you. At the same time, a low GRE score may not detract as much from your application package, making the GRE a safer choice. But if you think you can perform well, you are better off taking the GMAT since a strong GMAT score carries more weight than a strong GRE score.
3. How sure are you as to which degree you want to pursue? The GMAT is an entrance exam developed for business schools, while the GRE is a general test for graduates. If you are deliberating between an MBA and a different Masters degree, the GRE will keep all options on the table. However, if your mind is set on an MBA, the GMAT is most likely the test for you.
Check out: How to Plan Your GMAT and GRE Dates
This short video offers very useful and relevant advice. Check it out if you are still struggling to choose between the GMAT and the GRE.