He's worth noting, within the Blacks, because he's the Gryffindor. He's the odd one out. And it seems strange, that a boy from such a solidly Slytherin family would ever be a Gryffindor, but there's no doubt it's where he belongs. After all, he's recklessly brave, foolishly rash, and he will never do anything with great consideration. He believes in flying through life by the seat of his pants and hoping everything turns out okay in the end.
He's fiercely loyal, however, though he doesn't seem to realize that the trait that he prizes so highly is a Black trait through and through. Because, as a whole, the Blacks believe in loyalty above all – loyalty to blood. Sirius defied the trend in giving his loyalty to his friends, not his family, but it's still a Black trait.