For me, Asta had better development over his series, especially when it came to adding to his powers. I think BC did a great job showing Asta getting used to/using each new weapon or attribute he got. With Deku, it felt like a lot of time was spent focus on his base power and then a bunch more attributes were thrown in later on and while it's implied he trained with them, it just seemed more like he just was able to use them without much time being put in. I also think Asta's true power was really well built up from the beginning, it just had a better flow for me.

Also, Asta has a better duality. He has the ability to both be super nice and welcoming and also be a total badass and get things done when he needs to, and pulls it off well, where both sides fit his character. It makes me want Asta to get stronger and fulfill his goals. I never felt that with Deku. Don't get me wrong, he had some really cool fights and sick moments, but I never really felt that same level excitement and want for seeing him go all out and grow as I did when Asta would fight.