Whenever a threat arises that is mystical in nature and requires a response in kind, the Justice League relies on the Justice League Dark--a team of superheroes well-versed in magic and the paranormal. The team has gone through a couple of iterations but currently works in conjunction with the Justice League and is led by Wonder Woman. Zatanna, John Constantine, and Swamp Thing have been mainstays, with Detective Chimp and Man-Bat lending the team a hand these days. Deadman, Madame Xanadu, and Black Orchid have been members in the past.
A-Force is a team that first manifested in Doctor Doom's Battleworld during Jonathan Hickman's Secret Wars event, but, thanks to an extradimensional being named Singularity, was able to reform on Earth-616 after things went back to normal. She-Hulk, Captain Marvel, Medusa, Dazzler, and Nico Minoru were the five Singularity brought together for this team.
10 JUSTICE LEAGUE DARK: Unpredictability Of Magic
For the purposes of this list, the Justice League Dark lineup in question is going to be the post-No Justice lineup of Wonder Woman, Detective Chimp, Zatanna, John Constantine, Swamp Thing, and Man-Bat (even if Constantine departed not too far into the series), and the A-Force lineup is going to be the post-Secret Wars team of Captain Marvel, She-Hulk, Medusa, Dazzler, Nico Minoru, and Singularity.
While Nico gives A-Force a foot in the world of magic, the likes of Constantine, Zatanna, and Swamp Thing eat, sleep, and bleed magic (literally in some cases). They can tap into a world unimaginable to the likes of Carol and Medusa. Magic is weird, unpredictable, and frankly pretty scary. A-Force would have to shut Zatanna and Constantine down pretty quickly to even have a chance at winning this fight.
9 A-FORCE: They Have A Hulk
The Hulk is something else pretty scary and unpredictable, and A-Force has one on their side in Jen Walters. While She-Hulk has traditionally had more control than her cousin, she can still tap into her green side if things get rough. In fact, she's been bigger and meaner than ever in the current Jason Aaron, Ed McGuinness, and Paco Medina Avengers series. She can even create gamma detonations if things get especially spicy.
8 JUSTICE LEAGUE DARK: They Have A Wonder Woman
Of course, Justice League Dark is also led by one of the all-time greatest heroes: Wonder Woman. She is a warrior born, immensely strong, and a brilliant battle tactician. She fills the leader role of Justice League Dark, and A-Force doesn't have a true leader to counter that with two headstrong personalities like Captain Marvel and Medusa on the team. Wonder Woman is an edge that A-Force just can't quite match.
7 A-FORCE: The Good Captain
That said, Captain Marvel is pretty close to being a Wonder Woman figure for A-Force. She is also an immensely powerful individual with a history in a military role. She can tap into a deep well of cosmic energy which could potentially stop most of Justice League Dark in their tracks. She can also fly at near-light speeds, which would allow her to close the gap between herself and the likes of Constantine and Zatanna in less than a second.
6 JUSTICE LEAGUE DARK: The Hellblazer
John Constantine is another element that could potentially completely upend things. The Hellblazer is a major unknown in every conflict. He's cunning and often ruthless. He's willing to do things most of the superhero set aren't willing to replicate, and he could easily pull something out of his trenchcoat that would cripple A-Force--potentially permanently.
Even if the likes of Diana and Zatanna would rather John leave such tricks out of the fight, he might just decide to pull them out anyway.
5 A-FORCE: The Singularity
Singularity is an unknown all her own. She is a being who exists outside of our universe and can manipulate time and space. She has a childlike personality that leaves her also quite unpredictable despite her godlike abilities. She could also pull A-Force into herself if she feels that the team is in grave danger, and she has telepathic communication that can keep the team better coordinated than they would otherwise be. These abilities could also mess with Justice League Dark quite a bit.
4 JUSTICE LEAGUE DARK: The Edge Of Reality
The Justice League Dark has, of course, mixed it up with reality benders before. From Circe to Klarion to the Upside-Down Man, the Justice League Dark has explored the very edges of what is possible and beyond. The Upside-Down Man, in particular, has forced the team to reckon with the end of all things, and he has brought unimaginable chaos to our world. Being able to cope, let alone battle, with such things is a tremendous feat and could give the team an edge over A-Force, even with someone like Singularity on their side.
3 A-FORCE: A Team Of Many Worlds
In a way, A-Force has survived collapsing realities too. The team originally existed in one of the territories on Doctor Doom's Battleworld and still survived to exist in the world that came after thanks to Singularity. That's a powerful idea, and the team is extremely diverse in its composition. Captain Marvel is one of Earth's most powerful and popular heroes, She-Hulk is another Avenger who taps into the utter chaos of gamma energy, Medusa is Inhuman royalty, Dazzler is an X-Man popstar, and Nico Minoru is a Runaways sorceress. They make up many different worlds, and those different approaches to being a hero could be a force to be reckoned with for the Justice League Dark.
2 JUSTICE LEAGUE DARK: Saving Magic
The Justice League Dark is also trying to accomplish the insurmountable task of saving magic, and that takes a determination, imagination, and ingenuity few have. At the very least, this means they would likely be able to circumnavigate Nico Minoru's magical abilities. Detective Chimp and Man-Bat's own cleverness and curiosity will likely allow them to have a good analysis of A-Force's tactics and powers too, which would give them an advantage.
1 A-FORCE: They Actually Like One Another (Or At Least Don't Hate Each Other)
The difference-maker may just be, relatively speaking, that A-Force is a far more cohesive team. Captain Marvel and She-Hulk were already friends before the team even formed, and Singularity has gone a long way to bringing them together with Dazzler, Nico, and Medusa. By contrast, the Justice League Dark has always been an erstwhile team of necessity. Wonder Woman tries to bring them together, but Detective Chimp is a grouchy drunk, Man-Bat is a nervous intellectual, Swamp Thing doesn't get along well with flesh-and-blood folk, and Zatanna and John Constantine have bad blood. Plus, Constantine tends to make everyone hate him in general.