Its really to hard to say! I mean they are all very talented, but none is older than 16, and so it is really tough with these age restrictions. If one has a great tournament then her ranking will shoot up, but if another has a poor one, then they will have to wait til they can play a next event.
I suppose at this stage u have to favor the two that are ranked highest, Angie and Su-Wei...but Angie is not in great form at the moment and I think Su-Wei may in fact be the youngest of the bunch so she cant play many events! Apparently Sveta is mainly focusing on the Grand Slams (according to Eggy

) this year and I have no idea of what she is playing next, so maybe Gisella or Kaia may sneak in?
But as I said, with the age restrictions, its too tough for me to say...but I voted for Sveta anyway
I suppose it all comes down to playing well at the right time when ur that young on tour!