Before deciding on an MBA, I was considering getting an MPP (masters in public policy) and took the GRE. The math section is wayyy easier than the GMAT math (high school level, but no tricks at all), but the verbal is harder in some ways because you just have to memorize a ton of vocab. It took me 3 trys to get a decent verbal score (I think I ended up with a 650 out of 800, which is barely in the 90th percentile or something). The essays are also graded harder. My scores were all over the place for the 3 tests I took. I was considering submitting my GRE scores instead of taking the GMAT, but when I looked at the GRE averages of the schools that accepted the test, they were higher than my scores (the verbal specifically). So I took the GMAT. I think ETS has a translator for GRE scores into GMAT scores and mine ended up being what I eventually got on my GMAT. I recommend taking the GMAT for bschool - like someone mentioned above, future employers may want to know your scores for the GMAT. Schools started accepting the GRE to encourage people who may have been interested in another type of grad school to apply for MBA programs as well.
Overall, the only section easier than the GMAT is the math section (but also if you get like 770 out of 800, that puts you below the 90th percentile or around there). The GRE is cheaper though ($150) and there are fewer questions/shorter sections.