The scores for the GMAT and GRE are different thus it is difficult to compare the two. The GRE is cheaper than the GMAT, however, the format is different as well as the scoring. Additionally, the GRE is given in more geographical locations than the GMAT.
Moreover, each educational institution has their own separate guidelines for which exam they accept, so we suggest that you spend time doing research on the school that most interests you and looking at the exam they require for applicants.