I think by default I have to go with Mileena, seeing as she's the only one who has been showcased in any sort of fashion out of all of them. The rest we haven't really seen much on.
Not even sure why Sheeva is even an option considering we have heard absolutely nothing on her, so how could she be someone's favorite in the new game?
I mean in all the mortal kombats, besides, she will definitely be in the game =] you'll see.