Prepare for something long and dragged out :D.
Well to me personality is definitely shaped both ways, nature and nurture and I shall explain like this. Lets pretend a personality trait is like a seed, and the person, would represent the soil that these seeds are buried in. Now some seeds, no matter what kind of environment they lived in will grow to be tall trees, and this stuff would explain things like any talent or intelligence that comes to a person without much effort. Its also explains how person A and person B can both live in home C and turn out completely different, for example one being a decent person and the other being a horrible one.
Then there are seeds that the environment does shape, and big factors in shaping them are the parents, peers, teachers, etc. One thing that must be mentioned is the fact that the obvious things aren't always what shapes the kids the most.