Lets not get ahead of ourselves. Yeah, he's definitely the strongest villain option available for WW. . . but there is no way any such villain is competing with the Joker. The simple fact that the Joker has been part of popular culture for 60+ years ensures it.
But Ares has been a part of popular culture since such a thing existed. ZING!

But for real, Ares is at least an equally primal concept. If someone turns in a genius performance, he'll be right up there with Darth Vader, Joker and Hannibal Lecter.
Soooo, a sadistic misogynistic telepathic dwarf who does horrible things to women to get his jollies off is groan-worthy? I think you need to really stop and take a look at some of these characters before you write them off. Both WW and Flash have some of the more intriguing villains ever created. Especially Flashes Rogues. The Rogues are better than Spider-Man's overrated gaggle of animal themed lunatics.
That's the issue. The GA doesn't stop and take a look at characters. They get the one line summary, and if that comes down to guy with a heat ray, then how can they possibly ever regard him as a threat, no matter how well developed he is under Geoff Johns?
And yes, dwarf villains, especially misogyny poster boys are groan worthy. It's a very obvious 'see, he's trying to make up for something' thing.
For a first WW film, I think Ares is the most logical. But before we talk about villians, hopefully they can get the actress and the actual costume right. If they come up with anything close to resembling the costume they would have had for the tv show, they should just stop while they're ahead.
I disagree. Imho, Wonder Woman doesn't even need a costume if the story and villain are right. If all they have is a hot actress and a good costume, they're basically setting her up to be nothing more than a sex fantasy.
There are more villains, yes, but I have a hard time seeing them actually *work*. Circe, I suppose, but the rest would most likely come off as either totally random or groan-worthy.
Circe you
suppose? She's a area control/manipulative character spinning out of the mythology. She's very much the anti-Diana and she makes cool monsters to fight. Incidentally, since she makes were-animals, Cheetah could naturally spin out of that and not be random.
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On the OP:
For Wonder Woman: Ares (mastermind), The US Military (manipulated) and greek monsters (Cannon fodder) for the first one; Circe (simple mastermind ala Joker), Cheetah (manipulated combatant ala Two Face) and some wereanimals (cannon fodder) for the second one; Baroness Von Gunther (hardcore mastermind), Captain Nazi (simple brute) and some undead Nazis (you guessed it, fodder) for the third.
For Flash: Dr. Alchemy (Shared origin) and Captain Boomerang (simple serial killer) for the first one; Rogues Captain Cold (mastermind), Heat Wave (comic relief mook), Weather Wizard (Powerhouse), Golden Glider (love triangle) and Captain Boomerang for the second one; Zoom for the third one.
For Green Lantern (so not gonna happen): Sinestro and small Corps for the reboot; War of Light (greatly simplified, ie one member of each color) for the second one; Darkest Night for the third one;
Superman: assuming there's a sequel, Lex (mastermind) and Metallo and Bizzaro (Both Lexcorp products); Brainiac and Doomsday for the third one. it's pretty clear who's the mastermind and who's the grub in each one, eh?
Batman: would love to see it go more hyper-real in the reboot. Black Mask (crime boss turned freak) and Man Bat (geneTherapy success) in the first one. Mad Hatter (Subsonics) and Killer Croc (genetic monster) in a Robin spinoff. Riddler (FBI Batman hunter bait turned real criminal) and Poison Ivy (genetic experiment) in the second one, and yes, Clayface (no idea how to explain him) and Penguin in a third one. And keep going from there.
Justice League: Shot as one continuous movie and then split into three ala Lord of the Rings. Despero for the first one as we establish the team, Injustice Gang for the second one and Darkseid proper for the third, with Darkseid being responsible for everything. Note, this can be done, even if Superman/Batman/Wonder Woman/Flash are not available. You can do a JLI-ish version with Booster Gold, Blue Beetle, any GL, Fire, Ice, maybe Aquaman and Martian Manhunter.