First of all this is hypothetical and just for fun, I am in no way suggesting Riot should implement this.
Secondly the team max is 7.
Last of all, no more than two per region.
Personal opinion ahoy!
(Also, champ biases - could have had Jayce. Had Viktor instead. Wanted Ekko instead, but went with Taliyah for her more traditional innocence and innate powers.)
: The 'Face' (Underestimated, All Business)
: The Brains Behind the Scenes (Reluctant Leader)
: The One Willing To Do Terrible Things (If Necessary)
: The Muscle With Personality (Might Refuse Orders)
: The Young and Idealistic One (with Powers)
Headcanon; the dynamics would be:
Taliyah and Braum immediately become friends. Viktor and Nasus give each other a knowing look, ready to cut the rest loose for their own good when crap hits the fan. MF knows what Nasus and Viktor up to, even if they don't know she knows. She'll cut them loose if needed. MF tries to protect Taliyah from danger and tough decisions, but her actions are a real bad influence on the youth. It's killing Nasus to even have Taliyah on the team, in danger, but he needs her help and knows that Braum might leave if she goes too. Viktor respects the hell out of MF, using other people's weaknesses against them. Doesn't realize that's his weakness. People underestimate Braum. Viktor in particular who thinks he's a bit simple. He's not; he's just a good person and there's nothing wrong with that.Suicide Squad:
The poster Boy
The big gun
The Mage
The Better Mage
The pitied One
Revenge!
The Reason they win fights.
The fantastic 4:
The Fighter
The Tracker
The Sniper
The Muscle
The Healer and team "sweetheart"
The Sorceress
The "Dad" (and the only one who can cook. He's teaching Nami, though, and Morgana may be expressing interest. Braum is absolutely thrilled. Family time!).
Alternate team:
Team "Oh my goodness, how do I keep them from killing each other"
Technically Zac is a self proclaimed hero. They changed his lore recently so i dont know if its canon anymore. He wanted to bring peace and justice to Zaun.
-Charming and smart, coming up new tactics for combatting problems.
-Caring and shy, doesn't want to hurt anyone, but will do so for greater good. Has a lot of untapped power.
-Mysterious and destructive. He's a secret weapon that they don't let out of the cage much because of his.... Methods.
-A natural tactician. He's generally the de factob leader, but isn't afraid to ask for help.
-Comical. The funny guy. He's clumsy and always trying to prove to the others that he's worthy to be on the team.
-The creepy ones with strange words of wisdom. They've been around for ages and know a lot about the magical evils the team has to face constantly.
-The tough guy. Just like she says "Punch first, ask questions later."
Hulk
Iron Man
Captain America
Hawkeye
Thor
Black Widow
Team birb :D
I think they'd make a good super hero squad
(The random normal human without powes) 
(the science guy)
Or maybe
(?) 
(Super Villain who turns into a good guy for reasons) 
Going off more of lore than anything else, I'd picture a League Avengers like this:
Gotta give some honorary rewards to and here too but the main seven there are who I feel would be the most likely Avengers team: a group of people covering all manner of territories in Runeterra who have the means to be involved in conflicts and storylines the world over.
There aren't many champions as well travelled as these lot, with their overall goals being flexible enough that they're probably alright to drop things and team up: Nami and Taliyah can pretty much be free agents when their people are safe, Ezreal's only really focused on finding out his family's ultimate fate, and Ivern, Shen, Ryze and Diana are governed only by their overall responsibility to Runeterra itself.
Big Guy
Leader
Smart Guy
Lancer
Heart
Auxiliary members:
When she's not busy protecting her tribe.
When she's not busy being a policewoman.
Team Leader. Has seen the world come close to breaking, and leads the charge to see it saved and whole once again. Can be somewhat caustic, but is still trusted.
The Smart Guy. Knows way too much, and is willing to go to dark places to help the team. Not entirely trusted, but is surprisingly noble and sociable.
The Big Guy. Her dedication and strength help the team through the roughest situations. Secretly wonders which of her teammates is The Hero, and is banned from telling jokes at team meetings.
The Heart. A fierce warrior with an uplifting presence, she inspires the team and Runeterra to resist the darkness. Has a huge barbecue party planned if the team is successful.
Kai'Sa: The Co-Leader. Her adamantium will is the backbone of their battle plans, and she has the nerve to make the biggest sacrifices. Though still unused to formal functions, is the most approachable of the group after Leona and the next member.
The Tech Support. His ego interferes with directly assisting the team, but if it comes down to it he'll join them when the need is great.
The Loner. A member of the group for one reason and one reason only, Kayle is hesitant to mingle with the rest of the team outside of her specified terms.
Truly, a team of heroes from diverse backgrounds with a myriad of skills. But the dangers and temptations are great- if they don't save Runterra, they will be the ones to break it. And who/what are they resisting?
THE VILLAINS
Dark deals and shadowy meetings gave rise to The Riders and The Storm. Morgana, The Fallen Angel, contacted Kayn, Varus, Aatrox, the Darkin of the Depths, and the Darkin in the North and set out her plan: total domination and rule. To the unwise it would seem their campaign would merely bring destruction, but that is only to clear the way for their dark empire. With powerful magic, The Riders(that is, Morgana and the Darkin) have conjured The Storm, otherworldly beings from the depths of The Void and the grave, and unleashed them across Runeterra. An epoch of darkness and war awaits humanity, and the time to stop it is running out.
RANDOM HEADCANON -Jayce has a thing for Kai'Sa, though she is quick to shut his advances down. Is making a weaponized armor suit for her in secret.
-Swain is plotting to take the magic The Riders are using and turn it against them. Only Kayle knows this, but she merely advises to keep a close eye on Swain.
-Ryze has many internal debates over whether he should turn his world-breaking magic against The Riders or play it safe. Poppy tries to cheer him up with jokes and fails miserably.
-Leona is the one Poppy is closest to on the team consciously making an effort to appear as a Yordle in private with her. The two have long conversations late at night about heroism and heroes.
the leader with an abrasive personality, often at odds with the other members, but always respected for his strength of will and caring nature (even though he doesn't like to show it)
the level-headed sniper, providing support from the backlines and emotional stability in time of crisis
the muscle, who fights big bad guys all on his own and keeps the final boss at bay until the rest of the team is able to unite and fight together; his straightforwardness can be sometimes problematic
the tech support, always ready to test his newest gadgets on the battlefield, usually ending up in failure and providing comedic relief
the silent one, always acting on his own with disregard for the rest of the team; his help has always been crucial in time of needs, but the other members still wonder whether they can really trust him...
the egomaniac who always charges head-on into the fray, looking for his spotligh; he's in only for the fame, but his skills are undeniable, so the rest of the team puts up with him... barely
the young idealist, whose potential is matched only by her naivety
See, when I think of the Avengers (more specifically, the MCU Avengers), one of the main things that I connect with them is a general lack of political/government affiliation. While it is true that most of them in canon are American citizens, their responsibility is primarily to the people of the world. With that in mind, I made my list of champions centered around those with few few or no true political allegiances:
: This one is kinda obvious to me. He’s responsible for recovering the World Runes. He has no allegiance to any nation of any sort and works solely to protect the world.
: Jax is a battle-crazed veteran from a now non-existant nation that simply lives to fight and find a good challenge. Simple-minded but definitely seems like he’d fight for the greater good for enough hard-boiled eggs.
: I don’t think I have to spell this one out. Hulk Smash.
: Technically Piltovian, but doesn’t really care about where he’s from and is an overall nice guy... Even if he is a bit cocky at sometimes.
: Taric is literally responsible for protecting all of Valoran. Protecting Runeterra, in turn, would protect Valoran.
: Literally not from Runeterra and has no political affiliation because of it. Cares only about doling out justice and purging the wicked.
That’s what I got right now.
Main Team: 
Guardians of the Galaxy: 
Rocket and Groot: 
and
Hulk: , Wolverine: 
, Black Panther: 
, Doctor Strange:
New Generation team: 
and
Thanos:
So Syndra would be the mysterious one who no one really knows what happened with her Lux would be ridiculously happy, loving the team and fighting villains, however sometimes she feels lonely and not strong/important enough. Lux and Syndra would have this amazing love-hate relationship, they seem not to like each other but in reality they are really good friends. Leblanc would be the sneaky one, always playing secret with the villains and playing all these mind games, but sometimes she gets too caught up in playing these games and gets help from her team. Talon is the one that has some 'unfinished business' he has to take care of. Heimer is the brains, the smartest, coming up with cool and amazing things the team can take advantage is, however he lacks the sneaky and decieveness Leblanc has, so they complement [Thats a word right?] each other perfectly. Garen is the leader, he's smart, good fighter, heart in the right place, and is an excellent strategist. He's also great at working in teams, however sometimes he does get in conflicts with Syndra Leblanc or Talon because theyre; Rude or are not dedicated enough to the team. Leona would be everyone's friend, she is the only one who kinda knows who Syndra is, has the greatest girl talk with Lux, makes amazing jokes with Leblanc (and secretly enjoys how she plays mind games with villains), helps Talon with his 'unfinished business', may not be smart but can listen for hours how Heimer rambles on about his science stuff, and is respected by everyone like Garen, she helps Garen with the stress of leading this team, and encourages him. She would also 100% die for everyone on the team every single moment.
I have no idea where these characters are located, but I think I have: 1 Ionia 2 Demacia 2 Noxus 1 Zaun 1 Targon
Hm... I'd like to see the Justice League Of Legends versus the Injustice League (Unlimited) Of Legends. SeemsGood.
Batman:
Superman:
Wonder Woman:
The Flash: 
Aquaman: 
Martian Manhunter:
Green Lantern: 
(yes i know this is a cop out just because he has a green lantern)
versus
Deathstroke The Terminator:
Metallo:
Cheetah: 
Reverse Flash (I believe this one is Thawne): 
Black Adam (no other rival for Aquaman tbh): 
Chronos:
Solomon Grundy: 
I chose the Injustice League Unlimited because it had more options than the original Injustice League, and as such, could correlate with champions who otherwise would not fit.
