Another possibility is Clint Barton. He has his own set of moral dilemmas and has made some choices during his time as an Avenger that could make him question his worthiness of the shield. For example, if he had to make a difficult call that resulted in some collateral damage, he might feel this way.
Maybe it's a new character created in the fanfiction. A character who was brought into the Avengers under unusual circumstances, like being from an enemy faction initially but then defecting. They might feel that their past actions, despite their change of heart, mean they don't deserve the shield.
Maybe the character has made some mistakes in the past and feels unworthy of the shield, which represents honor and responsibility in the Avengers. For example, if they had once let their comrades down during a crucial mission.
Loki could be a great focus in a fanfiction involving both. He has a history with the Avengers, but his wily and unpredictable nature could lead to some interesting interactions with the Agents of Shield. He could be playing his own game, pretending to help both groups while actually having his own agenda. It would be fun to write about how the Agents and the Avengers try to figure out his true motives and keep him in check.
In Avengers fanfiction, Phil Coulson is often considered one of the best Shield agents. He is highly dedicated, intelligent, and has a deep understanding of the Avengers. Another great one could be Maria Hill. She is tough, strategic, and can handle high - pressure situations well. And then there's Clint Barton, who combines his excellent archery skills with his Shield agent training.
Often, in such fanfictions, the rogues might face consequences due to their own mistakes or being outsmarted by the Avengers' teamwork and superior skills. Also, sometimes external circumstances might play a role in their downfall.
Skills are a big part. Agents like Natasha Romanoff are great because of their combat skills. They can take on multiple opponents at once. Also, intelligence matters. Agents need to be able to analyze complex situations. For example, Phil Coulson who can quickly figure out what the Avengers need. And loyalty to Shield is crucial too.
I think the interaction between Coulson and Captain America would be really interesting. Coulson is a big fan of Captain America, and Steve would be impressed by Coulson's leadership and the way he holds his team together. They could exchange stories about their different experiences in the war - Steve from World War II and Coulson from more modern conflicts.
I think Daisy Johnson would be really interesting. She has her unique powers and a complex backstory from her time in SHIELD. In a crossover, she could interact with the likes of Thor. Maybe she could learn some new ways to control her powers from him, as he has experience with his own godly powers. And she could also show the Avengers her skills in combat and stealth that she learned in SHIELD. It would be fascinating to see how she holds her own among the super - powerful Avengers.
I think Natasha Romanoff and Melinda May would be an interesting pair. Both are strong, badass women with a lot of combat experience. They could share their stories of their past missions, and also train together. Maybe they could even have a friendly competition to see who is better at hand - to - hand combat or espionage.
One interesting storyline could be a crossover where Agents of Shield agents have to team up with the Avengers to stop a powerful alien threat that neither group could handle alone. This would involve a lot of character interactions, like Coulson trying to give orders to Iron Man or Natasha Romanoff teaching some of the Shield agents her spy skills.
Definitely Coulson. He has such a rich backstory and his relationship with both the Agents of Shield and the Avengers (in an indirect way) is very interesting. His resurrection in Agents of Shield also provides a lot of potential for fanfiction. You could explore how he copes with being brought back to life and his new purpose.