Kara Danvers aka Supergirl is one of the younger DC superheroes, and as such, she sometimes struggled to fit in with the more experienced and older heroes. Supergirl may not be as famous as her older cousin Superman but that never stopped her from fighting villains and winning countless battles.
Similar to Superman, she's usually friendly and well-spirited, kind to others, but she also can be impatient and impulsive, traits often associated with youth. Supergirl gets along well with most of the heroes, but if she traveled to the Marvel universe, she would hate some of its heroes and would only team-up with others.
10 Would Team-Up: Squirrel Girl
Making fun of Squirrel Girl seems like a given for many superheroes and comic book fans alike, but Squirrel Girl is actually pretty awesome and deserves much more love. Yes, her powers may not be the most impressive one when it comes to all the Marvel superheroes, but that doesn't mean that Squirrel Girl is useless in a fight.
After all, it doesn't matter how you defeat your enemy, as long as you can do it, and Squirrel Girl often won by sending the squirrels against villains. She's naturally optimistic and it's easy to imagine she and Supergirl would click almost immediately after meeting for the first time.
9 Would Hate: Iron Man
No offense to Tony Stark, he's brilliant and great at fighting, but he can also be difficult to get along with, and a downright bad person at times. His playboy persona most likely would leave Supergirl less than impressed, as well as Tony's tendency to openly say whatever he thinks, even when it's not polite.
Iron Man can also seem arrogant to people who don't know him, and sometimes to his friends and allies as well, so he and Kara would most likely butt heads since they're both stubborn. They could potentially fight well together but it's difficult to imagine they would like each other very much... or at all, really.
8 Would Team-Up: Ms. Marvel
Just like Supergirl, Kamala Khan aka Ms. Marvel is a younger superhero and she tries to live up to the image of a more experienced and known superhero (Captain Marvel), while at the same time building and maintaining her own identity as a superhero.
She and Kara have a lot in common and they would no doubt get along great and could go on many great adventures together as co-fighters. Kamala is a genuinely nice person who loves her family, her friends and the neighborhood she lives in and thanks to her civil and realistic mindset, she'd be a great companion to Kara.
7 Would Hate: Hulk
Supergirl and Bruce Banner might get along, united in their love for discovering new things. Even Professor Hulk and Supergirl could find common ground. But Hulk and Kara are unlikely to hit it off in a positive way. If Hulk went on a rampage induced by his anger, Kara would feel it as her duty to try and stop him to make sure that nobody would get hurt and that there would be no civilian casualties.
And as it's been demonstrated over and over again, both on the screen and in the comics, Hulk doesn't like it when someone beats him, which is exactly what Kara would most likely do.
6 Would Team-Up: Kitty Pryde
Another younger superhero on this list who would team-up with Supergirl and would find common ground with her is Kitty Pryde. Kitty is a member of X-Men and while there are a lot of X-Men members Supergirl could potentially be friends with, she and Kitty are the most likely ones to work together well both as a team and as friends.
Kitty is clever, friendly, has a sense of humor and she 's open to meeting new people, unlike some of her fellow X-Men. Her skills could also come in useful, especially since they're very different from what Supergirl can do.
5 Would Hate: Doctor Strange
Doctor Strange is an intriguing superhero. His skills could certainly come in handy if Kara had to deal with a villain possessing magical powers, but the problem is that while Doctor Strange is certainly a powerful superhero, as a person... he's difficult at times, to put it mildly.
He's often convinced that he's the only one who knows what they're doing, and that wouldn't sit well with Kara who wants to be independent and taken seriously as a superhero of her own right. Kara simply doesn't react well to arrogance, however, justified it might be, and just like with Iron Man, she and Doctor Strange wouldn't get along.
4 Would Team-Up: Spider-Man
There are multiple versions of Spider-Man that Supergirl could team up with, Miles Morales included, but let's focus on Peter Parker. When Peter first became a superhero, he was just as teenager, and similar in age to Kara. He has a strong sense of humor and usually enjoys being a superhero, the freedom that swinging around New York provides, and that's something Kara would appreciate after being forced to hide her powers for a long time.
Plus, their powers complement each other well, and if something bad happened, Kara can always fly Spider-Man to safety in case his webs wouldn't hold the web-slinger in the air anymore.
3 Would Hate: Deadpool
To say that Deadpool is a lot to take in would be an understatement of the century. He sometimes proves too much even for the most resilient and experienced heroes. Thanks to his regenerative abilities, he's difficult to get rid of, but the most annoying factor of Deadpool is his mouth, and the endless flow of flirtatious remarks, bad jokes, and insults that comes out of it.
Supergirl would most likely be seriously annoyed by Deadpool and she'd do her best to escape him but Deadpool can be so persistent that it's possible these two would actually end up fighting rather than teaming-up and taking on the bad guys together.
2 Would Team-Up: Captain America
There are many superheroes who are stronger than Captain America and have more special powers than him, but it'd still make sense if he and Supergirl would team up and if she instinctively trusted Captain America from the first meeting.
The reason for it is the fact that Captain America basically represents the same values as Supergirl's cousin Superman does and so working with Steve Rogers would feel very familiar and safe to Kara, almost like coming home. Steve is actually a nice guy for most of the time and he has a soft spot for young superhero so he'd probably take Kara under his protective wing (not that she needs it that much).
1 Would Hate: Punisher
Most superheroes are very decisive when it comes to killing people and they practice the "no killing" rule. But that's not the case for Punisher who has the rule that a good villain is a dead villain, which makes it difficult for him to work with most of the superhero world and has lead to conflict more than once.
It's safe to assume that Supergirl would feel similarly strongly about Punisher killing people, even those who had done bad things and could have deserved it. She might try and fight him and would win, which wouldn't help the relationship between the two.