I would definitively recommend SCHOLASTICA GMAT
They offer GMAT and GRE courses taught by mexican Harvard Alumni, who scored in the top percentile of the tests. Besides the strategy sessions, they guide you through all your GMAT or GRE preparation, they designed a personalized study plan that takes into account your daily study time, the deadlines of the programs you are interested in applying, and how far you are from your ideal score.
They also offer boutique admission consulting.
I also took their course and really love it! I highly recommend it.