It is clear that parents always want only the best for their children. The family does all it can to make the child successful by providing all the necessary assistance to the child. At any point where children are going in the wrong direction, parents will know the right way and help to understand all the mistakes, solve problems, give an important advice. It is also hard to deny that parents always accept their child as he or she really is and when the child meets his friends, who haven't been with him for such a long period of time as family, this is not the same case, and there is no doubt that peers can propose something contrary which will not be pleasing for both sides.
On the other hand, the teenagers often spend more of their time with their friends because they want to be away from the home environment, trying new pursuits and socialising. Teenagers usually choose friends who are like thenselves, and in spite of parents best intentions, teenagers can perceive criticism of their friends as personal criticism. It can also be argued that sometimes problems can develop when parents don't show an interest in what their children are doing and there is a breakdown in communication between children and parents. It this case teenagers may be guided by the opinion of their peers more than by the family's opinion.
In summary, I would say that every situation depends on certain circumstances and it is always individual. But in my view, family influence is the most important in teenagers lives.