Hm, where to start... I know the thread says to name one trait. But there are a lot that seem to be a recurring theme to me. I'll just go with the two things from off the top of my head.

I like jack-of-all-trades characters - ones who actually paid attention in school and can figure out most skills on their own, albeit not super well. Having twenty, thirty skills or so? Reasonable, so long as there's a reason why they know each thing that fits in with the backstory. Kids raised on farms, for instance, might know automotive and mechanical work, animal care, basic botany, wilderness medicine, construction, extremely basic engineering, and shooting.

They're usually assertive introverts of some sort, too.