Of the two, nurture has the greater influence except in very unusual cases.
There are some ways in which nature has a great influence. We all have distinct personalities even when we are born to and raised by the same parents. However, our nurture does more to impact our behavior. We can see this, for example, in the findings of scholars in the biosocial school of what causes crime. They find that people can be biologically inclined to commit crimes, but that those inclinations can be greatly impacted by the environment in which the person is raised. We can also see this in how children who are raised in a middle class environment tend to do better academically than those who are raised by people who are poorer.
While both do have an impact, nurture is clearly the more important.