Science GPA is more important because it is a better indicator of how well a student will be able to handle the science classes at medical school. However, the overall GPA is still important and should not be taken lightly. If you have an extremely high science GPA, but a low overall GPA, it will raise some red flags to medical school admissions committees.
Also remember that GPA is not the only factor that medical schools will look at. Another important factor for medical schools is your MCAT score.