I think it'll be Harry and Hermione because when she found out that he and Cho kissed under the miseltoe, she frowned. During the triwizard tourney she was extremely affectionate and congratulatory towards Harry after the second task. And she nearly completely ignored Krums accomplishment altogether. Also at the end of book four she kissed Harry on the cheek which she has not done with Ron or Viktor to our knowledge. And when Harry arrived at 12 Grimmauld place she shrieked and threw herself on him and embraced him in a hug. And she seemed to feel just a tad more hatred toward Umbridge than even Harry or Ron. Don't think that Umbridge forcing Harry to cut up his own hand didn't play a part in that hatred.
Moreover Hermione needs an equal or a superior. Only Harry fulfills that requirement. She is literally the best in the school save for one person, Harry. And this is a man she can fall for.
She could never fall for Ron. You read what she said in OoP, right after Harry made out with Cho in the D.A. room. "Ron you are the most insensitive wart I have ever had the misfortune to meet." She's a gryffindor not a slytherin which means that when she speaks to her friends and others she feels she can trust, it's always from her heart and mind truthfully and without fear or regret. She also said that he had the emotional range of a teaspoon at some point.
Hermione argues so fiercely with Ron because she wants him to grow emotionally and turn into a mature, sensitive, man, not because she's developing feelings for him. It's almost like a parent trying to teach a child to be an adult. Hermione could not possibly fall for someone she believes to be less mature and more insensitive than her.
I do believe Ron has probably developed feelings for her that he doesn't even realize he has.
I don't think Hermione will ever fall for Viktor Krum either because she was never really been around him enough for him to compete with Harry for Hermione's heart. She only KINDA hung out with him for one year.
Now Harry, I think, has not even realized her feelings for him yet because she is clever enough to hide them. And I think she hides her heart from Harry because she's young and she doesn't quite yet know how to deal with these feelings. She's mature but inexperienced in the ways of life and love.

This is why I think what I think.