How does Ponyboy's relationship with Darry and Soda differ?

From the text:

Soda tries to understand, at least, which is more than Darry does. But then, Soda is different from anybody; he understands everything, almost. Like he's never hollering at me all the time the way Darry is, or treating me as if I was six instead of fourteen. I love Soda more than I've ever loved anyone, even Mom and Dad. He's always happy-go-lucky and grinning, while Darry's hard and firm and rarely grins at all. But then, Darry's gone through a lot in his twenty years, grown up too fast. Sodapop'll never grow up at all. I don't know which way's the best. I'll find out one of these days.