User blog:Mode Sau/August vs Zeref

Who is stronger, August or Zeref? Some people are telling me that August is stronger than Zeref as he can manipulate more number of magic than Zeref. Even in the manga, Makarov states that August could be much more handful than Zeref even though Zeref being immortal and the darkest mage of all time. So I am very confused about who is stronger.