One way to categorizing fictional characters is by the character alignment system. Originating in the fantasy tabletop game Dungeons & Dragons, this system involves nine different alignments consisting of combinations of good, neutral, evil, lawful, and chaotic. Most anime characters can also be sorted into this system.
Let's take a look at one of these alignments: chaotic good. Chaotic good anime characters don't care about obeying rules or keeping order - they make their own rules, thank you very much. But while they don't feel the need to uphold structure, they're also well-meaning, kind folks who will do anything to help the people around them. If this sounds like nearly every shonen protagonist ever, that's because most shonen protagonists are chaotic good, which is why you'll see Luffy, Edward Elric, Ichigo Kurosaki, and more on this list.
These characters are a lot of fun, and though they can be frustrating to the more lawful among us, they're loyal where it counts. Which of these characters is the best? That's up to you to decide.
While Ichigo Kurosaki can usually be found helping others, he's insistent that he only does it on his own terms, not on those of other people. In fact, he'll even go so far as to help people who don't want his help - like when he rescues Rukia by destroying Soul Society's social structure, even though she asked him not to.
Katsuki Bakugo doesn't listen to anybody except himself, which makes him impossible to deal with on team missions. Nevertheless, he wants to be the greatest superhero the world has ever seen. Though this goal is partially based on a desire for power and glory, he also has a genuine desire to save people.
Luffy is a pirate, which means that he shuns the rules of society, and will happily break the law without a thought. Nevertheless, he'll do anything to help those in need.
Nothing says chaotic good like a willingness to try and bring your mother back from the dead using forbidden alchemy techniques. Edward Elric doesn't care about what's advisable or even possible, he's going to do whatever it takes to get to the outcome he believes is best.