The GMAT or the GRE?
Top business schools accept both so don’t just limit yourself to the GMAT. If you’re not worried about the exam registration fee, then register and take both. Submit the one that you do better on — that’s what I did at least (although my own story was less practically thought out and more a crazy whirlwind of spontaneity).
The only problem with taking both is that you have to prepare for both.
Personally though, I think the GRE is much simpler to prepare for, so if you’re short on time then that’s the one to pick. The GRE reminds me of the SATs in format and certain question types. There’s less prep work needed because it’s almost like any other standardized test you’ve taken growing up. Everything considered, the GRE is the easier test when considering structure and content.