Query about GMAT or GRE

Hi I have scored 309 in GRE and applying for schools which accepts both GRE or GMAT. Two months to apply .what wud be better Gre again taking the score to 320 (target score) or Gmat taking the score to 700 ......Gmat oreparation started a week ago Suggestion Gre Verbal 148 so i m not good at verbal ...