It doesn't help that she never really had a home city where villains established themselves. Writers kept moving her around because DC had no idea what to do with her, but they needed to publish books with her or they'd lose the rights to the Marston estate (simplified version). What also doesn't help is that for decades, adaptations didn't do her or her villains justice. Super Friends just had generic Cheetah, a reskinned Batman '66 Catwoman. Justice League was a great show but the creators never read a Wonder Woman comic in their life. Hades? Aresia? Felix Faust? Actual Wonder Woman villains like Giganta and Cheetah were completely detached from her.
As for the comics, Ares/Mars is her most consistent enemy, though he's also been reimagined many different times.
All the Cheetahs are popular, though that's just a thief who happens to face Wonder Woman, like Catwoman for Batman - not a foil. A go-to villain in adaptations because of her function in Super Friends.
Circe has been prominent, but only since the late 1980s and she hasn't been used effectively in the New 52. She was a major player in the Wein/Perez run, Messner-Loebs' Boston arch, Jimenez' civil war and the whole Amazons Attack debacle. DC Universe Online made her the main enemy for Diana. Barring the gods I'd count her the most fleshed out Wonder Woman villain.
Other foils are Veronica Cale (her Lex Luthor), Genocide (her Bizarro), and Devastation (her Black Adam).
