Good question. As with most good questions, the answer is, "It depends."
I think in many cases peer pressure gets to kids more than parental pressure. In most homes, kids take their parents' love and acceptance for granted, it's a given, and hopefully the kid doesn't have to do a whole lot to keep that love and acceptance. But with peers, it's an entirely different story. For most of us, peer acceptance is a very important thing in adolescence, and peers don't accept us unconditionally, like a parent does. We have to do certain things, or act in certain ways, to earn that peer acceptance. Depending on which social groups we want to belong to, peer acceptance can hinge on many different things, some of which are not necessarily good things (drug use, sexual promiscuity, etc.). So we many do things that are not in our own best interest to gain acceptance. This is not normally the case with parental pressure.