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).

It's been suggested that Marston intended Dr. Psycho to be her nemesis, but he has never been utilised well in modern comics. In my mind he's the best choice but he needs to be written well and as more of an actual match for her.

The Harley Quinn TV show ruined any chance of that.

How do you mean? Cos I would actually say that one of the great things about HQ was the depiction of Psycho and how well they adapted the character and they even call him WW's nemesis

They play it for laughs on Harley Quinn but the misogyny is problematic if you translate him into anything else.

He's a very powerful and very dangerous incel.

^^ Well no I don't think so at all. Feminism and misogyny are core themes of wonder woman and an explicitly misogynistically motivated nemesis is what she needs imo.

In fact that actually WAS the original idea behind the character of doctor psycho. Wonder Woman was a feminist superhero so Dr. Psycho was designed with the explicit motivation of hating women.

@Tupka217 yeah and I think the stories need to lean into that even more. He's arguably more relevant now than he's ever been.

Ares

Either Ares, Circe or Cheetah