Definitely Naruto. His positive attitude and strong will could create a really interesting dynamic with Venom. He could either try to reform Venom or use its power for good in the Naruto world.
A crossover could work by having a common enemy. Let's say there is an entity that wants to take over both universes. Naruto and Agent Venom would meet while investigating this threat. They would find that their powers complement each other. Naruto's ability to create multiple clones could be used as a distraction while Agent Venom sneaks up on the enemy. Agent Venom's resistance to physical damage could also protect Naruto in dangerous situations. Their relationship could start off rocky due to differences in their personalities and fighting styles, but they would gradually learn to work together as they face greater challenges.
One possible plot could be that Venom somehow gets transported to the Naruto universe. He might initially be seen as a strange and powerful beast. Naruto, being the curious and friendly ninja he is, tries to communicate with Venom. They could end up teaming up against a common enemy like Orochimaru who is interested in Venom's powers for his own dark experiments.
In a Naruto and Venom crossover fanfic, the power balance would be crucial. Venom has superhuman strength, speed, and the ability to shapeshift. Naruto has his own set of powerful jutsu. You could have them team up against a common enemy, like an evil ninja who has also harnessed some dark symbiotic power. They would have to learn to work together, with Naruto teaching Venom about the ways of the ninja, and Venom showing Naruto some new combat techniques based on his powers.
At first, Venom might be angry at Naruto for neglecting it. But as the story progresses, Naruto could realize his mistake. Maybe he sees Venom helping the villagers in some way, like protecting them from a minor threat. This could make Naruto approach Venom and try to make amends. They could then start to train together, with Naruto teaching Venom about chakra and Venom teaching Naruto about its unique abilities.
There are likely 'Naruto is Venom' fanfictions out there. In them, the story might explore how Naruto copes with the alien entity inside him. The Venom symbiote in the Naruto universe could create some really unique scenarios. Maybe Naruto has to fight against the more violent tendencies of the symbiote while still using its power to protect his village. It could also introduce new villains or allies related to the symbiote's origin.
I think Spider - Man would be really interesting. Since in the comics, Venom has a long history with Spider - Man, and if you bring that into the Avengers' world, it could add a whole new layer of drama. The Avengers would be caught in the middle of their relationship, not fully understanding the complex history between them.
One idea could be a Venom crossover with Spider - Man in an alternate universe where they have to team up against a common enemy like Carnage. Another could be a Venom and Deadpool crossover, with their crazy personalities clashing and then somehow working together. Maybe a Venom crossover with the X - Men, where Venom's alien nature causes some interesting reactions among the mutants.
One possible storyline could be Venom getting involved in an Avengers mission. Maybe Venom's unique abilities like his symbiotic powers and super strength could be used to help the Avengers against a common enemy. For example, against a powerful alien threat that the Avengers alone can't handle. Venom's ability to blend into the shadows and his near - indestructibility could give the Avengers an edge in battle.
One common theme is the clash of ideologies. Venom has a more chaotic and anti - hero approach compared to the Avengers' heroic and morally upright stance. Another theme is redemption. Sometimes Venom is on a path to redeem himself through his interactions with the Avengers.