Michelle Obama is a very likable person. With her great smile and warm personality, she comes across like your favorite Aunt, who you know has your best interests at heart. When she tells us to grow a garden and eat healthy, we have to agree with her good advice. When she tells us to exercise and become healthy, and to teach our children the same, we agree again. When she tells us to work harder on reducing teen pregnancy, we agree with her yet again, but there is more than that. We see her supporting her husband's Teen Prevention Initiative, and we see her as the mother of two preteen girls with a potentially personal stake in this battle. The battle to bring up her own her own children in a way that protects them from the difficulties of Teen Pregnancy makes her "one of us". We are in this together. She is not an older woman with grown children who no longer has to face the posibility of teen daughters coming home pregnant one day. For these reasons, I think Michelle Obama would be an effective advocate against teen pregnancy.

Bristol Palin is the nation's most identifiable teen mother. Who better to tell other teens how it really is? After her success on Dancing with the stars, The Candie's foundation asked her and Mike "The Situation" to team up for a PSA aimed at preventing teen pregnancy through both abstinence and safe sex. The idea that Palin has vowed to remain abstinant is presented as a respectable choice, while Mike's reliance on big gold wrapped condoms while he chooses anything BUT abstinance basically covers all the bases in presenting a message very likely to strike a chord with the target audience, teens.

Here's one of the ads with just Palin, in the Pause before you Play campaign:
http://www.youtube.com/watch?v=YpHlztPeHf8&feature=related

sources:
http://www.medicalnewstoday.com/articles/215653.php
http://today.msnbc.msn.com/id/30597615/ns/today-parenting/
http://www.candiesfoundation.org/