my two cents quickly.
Karlie has presence. like it or not, the girl is a star. i definitely think her body needs to mature before she can really represent VS in a way that would match the Angels of the past. I don't see her landing the "male demographic" that really is very important for the biggest of VS's stars. Tyra, Laetitia, Heidi, Gisele, KK and Adriana have all been voted "Sexiest Alive" on some list or another. And they all have bombshell bodies. That really is key to being a star for VS. Karlie has ALL of the other qualities, I think. SO her potential is MASSIVE. she just has to mature into it a bit.
Shanina -- have never heard of her before. Had never seen her before. Am literally dumbstruck by her unreal beauty. She's a mix of Ashwarya Rai and Irena Sheik and she's sexy and classy at the same time. VS needs to get her in their rotation and in their catalogue and try to develop this girl. She could be big.
Joan. SHE is the next star of VS. Honestly - for a mass market company like VS, any of the ethnic girls have to have an accessible beauty in order to become massive spokesmodels for the brand. Tyra had it. and Joan has it. She is exotic looking and sexy and incredibly charismatic. and that body is crazy! she harkens back to the glamazons of the past. i am in love with this girl. she needs to be made into an Angel pronto.