Rodgers, Vick, or Peterson?

I am in a fantasy football league where you are allowed to keep ONLY ONE player from your previous roster for the next season at the same price you had payed for them in the previous year. We do an auction to get our players and you start with a $100 salary cap. Last year i somehow managed to get my hands on Adrian Peterson, Michael Vick, and Aaron Rodgers all of which i could keep but i can't decide who would best. Adrian Peterson would cost $15, Michael Vick would cost $10, and Aaron Rodgers would cost $12. Who do you think would be the best decision, please explain why you chose who you did. Thanks!