It is the thief. So, no strictly white box for me. I like the other classes, too, and though I'm not prejudiced against one or the other, somehow I like the thief class best.
It's the probably about the climbing sheer surfaces, disarming traps, and other neat
Thieves can be pretty versatile characters. Female thieves rock. Taking my favourite playable character race into account, I'd pick a human female thief.