Hi RealEstateMBA,
To start, you should confirm that the Schools/Programs that you are interested in will accept both Exam Scores as part of the application process. Assuming that the Programs do accept both, then there is something to be said for choosing the Exam that will allow you to best perform at a high level. The only practical way to assess your 'ability level' in either case is to take a FULL-LENGTH Practice Test under realistic testing conditions (a "mini" version simply won't match-up). Many Test-takers are unhappy with their initial practice scores, but you really shouldn't be thinking in those terms. That initial result would just be a measure of your skills right now - and you'll improve on that result over time as you learn more about the content, Tactics and little 'secrets' of whichever Exam you choose to focus on. To get a better 'feel' for each Test, you might find it useful to do some practice questions in each of the major question types before taking your Practice Exam (but regardless of which Exam you ultimately choose, you shouldn't take too long to take that first Practice Test).
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on your timeline and your goals:
1) Have you done any studying yet for the GMAT or GRE? If you have, then for how long and what materials have you used?
2) What is your overall goal score?
3) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich