Hi! I am also preparing for MBA. I have been told that some of the University still prefers GMAT over GRE although GRE is accepted too. It depends on the University you are eligible to apply to and the field in which you want to specialize in.. I have been preparing for GMAT after I took a counseling session at The Chopras who recommended me the names of Universities accordingly.
The minimum GRE score accepted is 300 or GMAT equivalent of 500. Hope this helps.