Heroes from the Marvel Universe often are created with flaws to help endear them to the audience. For Peter Parker having to fight off an attack by the Green Goblin at the risk of being late for school lets the audience in on the constant stress that he is under to maintain his superhero life and his normal life. If a hero were to turn to the dark side, sometimes it's easy to see why.
Contrast that to the DC Universe where characters such as Superman seem to be able to juggle everything thrown at them with no problem. If a hero were to take up residence in that universe could their flaws actually create a great villain?
10 Rogue
Rogue started out as a villain but quickly made the transition to a hero. Her mutant ability of being able to drain another hero's powers into herself would make her a top grade villain in the DC Universe. She could easily stand toe to toe with the likes of Superman. Take the memories and knowledge of the greatest detective in Batman to anticipate his every move.
She would also be able to destroy everyone's secret identities with a single touch. A match up with Wonder Woman would be her biggest challenge. How does Rogue handle taking on the powers of Zeus' daughter? She would be one of the biggest threats to the DC Universe.
9 The Hulk
Would a move to the DC Universe cause enough anger to put Bruce Banner into a permanent Hulk state? During three previous crossovers with Marvel and DC Superman he has come out on the losing end but what if Lex Luthor took an interest in Banner? Infusing him with Kryptonite radiation to boost his already high level of Gamma Radiation makes Hulk emit a power dampening field around him to face off against the Man Of Steel.
Even with Batman's intelligence, the Flash's speed, and Wonder Woman's power, it would be hard to stave off a Hulk who is permanently angry. If the brute can think through his rage then teaming up with the rest of the Legion of Doom would spell the end of the heroes of DC.
8 Black Widow
International assassinations, espionage, and spying seem perfect for someone in the Suicide Squad. While she started as a villain who came around to be a hero she could still do a lot of damage if her brainwashing were to take over. A.R.G.U.S. could send her out on numerous missions that end up putting her in the crosshairs of Green Arrow.
After her fight with Black Canary, the heroes would learn quickly that she is not one to be messed with. She has no qualms about taking a life to complete her mission and can go toe to toe with heroes such as Batman, Deathstroke, and the aforementioned Black Canary. She would not be a villain any hero would want to face off with.
7 The Thing
After being disfigured in an accident in space, Ben Grimm would go on a rampage. He blames his flight partner Hal Jordan and starts a lifelong vendetta. While the yellow impurity has been purged from the rings if The Thing's hue leaned more towards the yellow side it would be a great foil for early years Green Lantern stories.
With the introduction of the Red Lanterns, Ben Richards could easily take up the mantle of the angry ones and continue his feud with Jordan. He already would have been hard to contain but with his red ring, he would be nearly unstoppable. The JLA would be in deep trouble whenever he stepped foot back on earth.
6 Daredevil
As a young man, Matt Murdock gets blinded by toxic waste after a car accident that is caused by a young Batman fighting against some bank robbers. After being told he will never see again he vows vengeance against the Caped Crusader. Using his new radar senses he trains his body to become the ultimate fighter.
This would totally work and would attack Batman on the level of a martial mrtist and also his deduction skills. He may not have the wealth of Batman but he has a vendetta to keep him training and sharpening his skills. Daredevil could be the ultimate Batman villain if fate were to put them at odds.
5 Ghost Rider
Johnny Blaze worked in the same circus as Dick Grayson but after selling his soul to become the best trick rider ever he now has to collect souls for the devil under the persona as Ghost Rider. He would be a great addition to the supernatural side of the DC Universe. Crossing paths with John Constantine, they could fight for the souls of the living.
With the use of magic in DC, he could be a foe for a lot of the DC heroes such as Doctor Fate, Etrigan The Demon, or The Spectre. His penance stare and burning touch would create some great visuals for his showdowns. Plus who wouldn't want to see that burning Hellcycle heading down a Gotham street going straight at the Batmobile?
4 Emma Frost
While she does go back and forth between being a hero and a villain Emma Frost can be the biggest bad when she wants to. In her diamond form, she would be unbreakable for any hero that tried to stop her. Her psychic powers would be unmatched as she took her place among the DC villains. Even Gorilla Grodd would have to bow before her.
Hal Jordan's willpower would be tested against Emma as she attacked his mind. Her diamond form refracts light which could be worked into causing issues with the Green Lantern constructs. New weaknesses happen all the time. Gotta keep those threats fresh.
3 Bucky The Winter Soldier
Bucky has always been a top-notch soldier but after getting brainwashed by Checkmate he found himself at odds with the Suicide Squad. While pulling off political assassinations he catches the eye of Amanda Waller and is put on their hit list right away. He is a strategist on the level of Batman which would create a great back and forth between them.
A showdown of soldier vs soldier between Bucky and John Stewart could show a great side we haven't had much insight into with that Green Lantern. Stewart is able to construct weapons with his ring but Bucky is a master at taking down someone with what he has available around him. Each soldier would bring a lot of things to the table but Stewart wouldn't be walking away unscathed.
2 Wolverine
The Cadmus Project began experimenting on soldiers to create the ultimate supersoldier and Logan was the only man to survive. After breaking out of the lab he went on a rage-fueled killing spree. He was finally stopped by members of the JLA who thought they had incapacitated him. Turns out he has a super-fast healing factor.
With adamantium claws, he is even a danger to Superman himself. It would take a whole lot to contain him even with a whole team trying to stop him. If a hero were ever to go against the Wolverine's feral rage they would find themselves in a sorry state. Hopefully, as his mind cleared he would realize his rage was misdirected at the heroes of DC but getting him to that point would take a lot of work.
1 The Punisher
This one doesn't take a lot to consider. He's already at odds with how just about every hero in both the Marvel and DC universes. Using his version of justice, Batman would have a big problem with a vigilante gunning down mobsters in Gotham City. On opposite sides of the debate, Frank Castle would have no problem putting a few more holes in that cape.
His military experience would come in handy against the wealthiest superhero on the planet. Defending against all of Batman's gadgets would be his top priority while taking it to the Caped Crusader to throw him off balance. His goal of taking out all organized crime in the DC Universe would pit him against a lot of heroes who appreciate his goal but don't like the way he's going about it.