OVC has a different rating system for Hips that I (personally) don't like. OVC gives your Hips a Pass or Fail, that's it. OFA however, will give you a definate grade, F=Fair G=Good E=Excellent. It may cost more, but IMO worth more.
I also would like to add thet CERF exams on Breeding Stock should be done every year. My Dog passed his first CERF, but failed each consecutive test, so this would be critical information if I were to be using him at Stud.