Compare to what? If you're talking each other, then unit to unit the Vex are better but Oryx and his siblings are so incredibly powerful that the Vex have already accepted the fact that unless something completely unforeseeable happens (like guardians killing Oryx) that the Vex will inevitably be consumed by Oryx. If you're asking how the Hive and Vex compare to the Forerunners or Precursors, that's not even fair. The Forerunners alone are many times more powerful and advanced than either the Hive or Vex and the Precursors are basically gods, able to control the very laws and fabric of reality and life at will.