Thanks for your inquiry!
In terms of the GRE vs GMAT, the biggest drawback to taking the GRE is that business schools are only recently starting to accept it, so not as many do. If you are applying to several schools, there's a pretty good chance that at least one will not take the GRE, and thus you'll end up having to take the GMAT anyway!
If you have verified that all the schools you're applying to take the GRE, then there shouldn't be any advantages or disadvantages. The school isn't offering the GRE option as a way to evaluate candidates in terms of which exam the candidates choose; they consider it a good reflection of your abilities. So then it comes down to which exam you're more comfortable with and feel best reflects your abilities.
Good luck!
Jessica Shklar
Senior Consultant
mbaMission
www.mbamission.com