I think Izuku Midoriya would be really interesting. He's the main character and has so much knowledge about the heroes and villains. If he time - travels, he could use his understanding of quirks and combat strategies to change the past or future in significant ways. For example, he could go back and give advice to All Might when he was younger, which might change how All Might deals with villains later on.
Katsuki Bakugo could also be great for time - travel. His hot - headed nature and powerful quirk would make for some intense time - traveling scenarios. He could go back in time and perhaps compete with the older generation of heroes, learning from them in a more hands - on way. Or he could travel to the future and see the consequences of his actions in the present, which might make him change his ways in the present.
I think Zoro would be really interesting to time travel. He has a strong sense of honor and his swordsmanship skills are top - notch. If he traveled to the past, he could learn from the greatest swordsmen of that era and bring back ancient sword techniques to the present. In the future, he could see how swordsmanship has evolved and maybe even find a way to further enhance his own skills.
Kazama Chikage might be an interesting choice as well. He is a powerful and somewhat arrogant character. If he time - travels, perhaps to a past era where his clan was even more powerful, he could try to change history to make his clan even more dominant. Or if he travels to a future where his power is nothing compared to modern technology, his struggle to come to terms with his new position in the world would be an interesting plotline.
Iroh would be fascinating to see time - traveling. He has so much wisdom already. If he traveled to different times, he could share his knowledge and perhaps change some key events. He could also gain more insights from other time periods, which would further enrich his already deep understanding of the world.
Daenerys Targaryen. She has a strong will and a mission to claim the Iron Throne. If she time - traveled, she could meet her ancestors and learn from their successes and failures. She could also try to prevent the downfall of her family in the past, which would have a huge impact on the present state of Westeros in the fanfiction world.
Ahsoka Tano would be a great choice. She has a complex history within the Clone Wars. If she were to travel back in time, she could interact with her younger self. She might be able to pass on wisdom she gained from her later experiences, like how to better handle the politics within the Jedi Order and the Galactic Republic.
Ruby would be really interesting. Since she's the main character, seeing her go back in time and interact with her younger self or her mother could be really emotional and full of character development. She could also use her knowledge to make herself an even better Huntress at an earlier age.
Lip would be really interesting. He's smart but has his own set of problems. If he could time - travel, he might go back to fix some of his mistakes, like not taking better care of Fiona or making better choices in his relationships. He could use his intelligence to change things for the better in the past.
Midoriya would be a likely candidate. He's always looking for ways to improve and become a better hero. Time travel could give him the chance to learn from past heroes directly, like All Might in his prime. He could also go back to understand more about One for All's past users and how to master the quirk faster.
Eleven could be a likely candidate. Given her powerful psychic abilities, she might accidentally or purposefully time travel. Her powers have always been a bit unpredictable, and time travel could be an extension of that. She has a strong connection to the Upside Down, so she might be sent back in time to learn more about its origin or how to stop it.
Shikamaru might be the most influential. He is known for his intelligence. In a time travel situation, he could quickly analyze the situation, come up with plans, and predict the consequences of different actions. His strategic mind would be crucial in dealing with any unexpected events during the time travel, whether it's in the past or the future.