Christina Aguilera, by far. She has the most potential out of ALL of the choices listed and she's been working with hitmaker Max Martin, all cards are on her side.
Keri, Ciara and Cassie are done. Bey isn't releasing an album this year. I think Xtina and Avril will both go top 10 with their next single so whoever releaases first. I voted Avril because she's the Queen.