In my opinion, this question is debated for a simple reason -- it is because it can never be answered.
In my opinion, personality traits are strongly influenced by both of these things. There is no way that people are not influenced by their genes, but there are strong influences that come from one's surroundings.
Anyone who has more than one child should know that genes matter. One of my kids is naturally angrier than the other. At the same time, they have, by growing up together, rubbed off on each other and have also been influenced, I think, by our parenting.