I suppose I favor nature more than nurture although in different societies gender roles are very different from what you find in the United States. Even in the US there are a variety of thoughts on gender roles depending on the parents and their background. Speaking from experience, both from my own childhood and now raising my son, I think it is largely nature with pressure from society to be one way or another. I was very boyish as a child and teenager and rarely identified with any of the typical things associated with women. My mother thought I was actually homosexual for a long time, which annoyed me honestly. Also it was harder for me to make friends because most people thought I was pretty weird for not being the typical girl.
Now I am a stay-at-home mother, and guess what? I love it. I am still in many ways not a typical 'woman' but the way I was raised, I was allowed to think for myself. I don't let society dictate how I should behave one way or another. My son seems to be 110% boy almost all the time, but he stills like to play with dolls or other toys that are supposed to be for girls. I think it is ridiculous not to allow your child the freedom to make his or her own choices, especially about something that is so intrinsically designed into each person. It depends on how you are raised, either to think for yourself and do what is going to work for you and whatever your standards are, or to let society tell you how to act. This can go both ways, forcing either gender into roles that do not work for them. I will not feel guilty for loving my role as a stay at home mother, or for enjoying to shop for clothing and shoes, liking baby animals, or whatever other silly preconceived notions there are for woman. Similarly men should not feel guilty for wanting to feel manly, for wanting to be a sole provider for their family, for enjoying sports, or any other thing typically associated with men. Neither should either gender feel like they cannot enjoy the things that the other gender enjoys, or play a similar role in life as the other gender.