I have always thought (or wanted) Cheetah was her archenemy.
She's one of the first costumed villains Diana faced and, in Barbara Minerva's case, she was cursed by the Gods which contrast nicely with Diana being blessed by them. Besides, she can fight face to face with Diana without help which also contrast with her warrior's nature.
I have always seen Ares and Circe as WW's Brainiac or Doomsday. Huge and powerful threats who could destroy the world if they want to, but Cheetah would be a more personal enemy.