Gmat,cat,gre tests your analytical and reasoning skills. Gmat is for overseas mba. Cat is only restricted to Indian b-schools mba or PhD. Gre is for overseas masters and PhD degrees. Gmat and Gre will have a wider coverage since it is overseas/global. Cat will be narrowed only within India. Gmat,Gre will give you wider options to choose a reputed institute. Overseas studies will be more expensive than cat studies. However, the ROI will be higher post gmat,gre. Overseas education will give you international exposure.