Personality is largely irrelevant to a good character. It's whether or not there's a reason for them to act that way and whether or not that reason is believable. In this sense there are a lot of characters that fall far short of the mark.

I think Yuffie is an example of a decent character. (Just an example I plucked out of the air.) She's distrustful and aggressive because her homeland was invaded and its greatness diminished (by ShinRa no less). She acts bouncy and hyperactive to cover up her insecurities about not being strong enough to please her father, and not being strong enough to help her village (a burden she places on herself).