It has to be between Sveta and Maria IMO. The other have all been Top players for over a year.
Elena D can be inconsistent but from RG onwards, her results have been pretty consistent except Wimby (pretty explainable) and her loss to Dulko. Plus the girl reached 2 GS finals in ONE year. Definitely Top 10 material and many Top 10 wins this year (something she couldn't do in the past).
Maria is hyped a lot, she does have a great game... for grass. Where she is extended into rallies, she can be effectively manouvered out of position. And you can begin to break down her power game. A serve, BH and FH are very important, but so is speed and variety in today's tennis. I think too many people expect her to win multiple Slams and become a No. 1. Let her grow.
Sveta. She played awesome in the final. But it was just a big serve and big forehand combination. And she herself said it was a good day as all her forehands were going in. That doesn't sound to me like a solid game plan. Sure she did well, but she played an injured player with a serve that got the treatment it deserves. And I truly believe that if Lindsay were not injured, she would have won the USO.
People are already touting Sveta and Maria as the next best thing, but these girls need more time to develop and that may involve a slide or slump along the way.
All the other girls have proved themselves IMO as they have been around for a long time.