What about Doutzen? I think she's gorgeous and she has the type of sex appeal that'll appeal to all, lets not forget men account for 50% of the population and if you want to be a household name you have to appeal to everyone.
With the CK Eternity ads and VS runway show, and Valentino's love for her.. I can really see her becoming huge in the next couple of years.
IMO I love Daria and Gemma and Stam, but I don't really see them becoming the next Giselle anytime soon. I think Daria can make it big, but in a Shalom Harlow kind of way (if that makes sense..), she'll be a legend in the fashion industry, but a relatively lowkey celebrity in the mainstream world. Gemma is one of a kind, but if she is going to make it big she is going to do it with her acting talent or something, I think her look is too polarizing for the mainstream. Stam is gorgeous to me, and I really like her look, but many people find her look off-putting.
I think Natalia would have a great shot, but I think maybe she's content with being the supermodel / NYC celebrity.. and there's nothing wrong with that, she's married and has wondeful children.
Overall my bet would be on Doutzen.