I will go with Allen Walker for many reasons. He is not brain dead character who will rush on enemies without strategy. Also he is not someone who will judge people for "evil" acts, like liying or just do some leather bad things. In same time he is not evil so eventually you will start emphatize with his character.
Allen Walker is deep character that has interesting, depressing backstory so in manga he never acted like another shounen hero. His character resemples "Pierro", or said clown, who is faking everything about him. Even his smile was always full of lie, case eventually his character development lead him to suicidal actions and motives. While eventually story crushed him in many ways, so even his main goal, even his believes was destroyed. Especially in the last chapters his story and his character development made him even deeper then before, when he understood that his whole life story was nothing but lies. But even when that happened, he didn't betray himself, he didn't felt hatred, or desire became evil beign. He continued to walk road that he choise himself.
In same time, Allen has his normal hero moments when he is trying to do things right and fight for goodness. So he isnot some ammoral chatacter who wants whole world burn.
His story could be described as tragedy from the very begining to the very end.
Allen Walker is deep character that has interesting, depressing backstory so in manga he never acted like another shounen hero. His character resemples "Pierro", or said clown, who is faking everything about him. Even his smile was always full of lie, case eventually his character development lead him to suicidal actions and motives. While eventually story crushed him in many ways, so even his main goal, even his believes was destroyed. Especially in the last chapters his story and his character development made him even deeper then before, when he understood that his whole life story was nothing but lies. But even when that happened, he didn't betray himself, he didn't felt hatred, or desire became evil beign. He continued to walk road that he choise himself.
In same time, Allen has his normal hero moments when he is trying to do things right and fight for goodness. So he isnot some ammoral chatacter who wants whole world burn.
His story could be described as tragedy from the very begining to the very end.
I love his relationship with Mana. My fav clowns in the whole world ❤️
Thorfinn is the definition of "character growth/development"
Thorfinns character is like a journey and you feel every step of it. Vinland Saga taught me a lot and it felt like my own personality also grew
My fav line, it gave me hope during my depression

Musashi is also a peak MC. I love everything about him. It’s similar to Thorfinn, my own personality grew with Musashi together.
Gintoki is underrated and is after Allen Walker my fav Shonen MC. He’s an idiot with a big heart. His backstory is 10/10 and his character has a lot of layers.Gintoki would be my ideal friend because our personality is nearly the same.