Well, what I mean is that, while she seems to be angry most of the time, and when she's not, she's annoyingly happy. But compare that to how Bella looks throughout most of the Twilight series. She seems kind of uninterested, actually. So, really, it's not really something Yuna does "right" as much as something she does better than Bella.
I hate them both with a vengeance, but if I had to choose, I'd pick Yuna...After a decade of resisting the choice, of course.