I've only seen the movies but to me Ron and Hermione didn't act like much of a couple, but Harry and Nermione seemed to have a perfect chemistry. They looked like a couple especially during the dance scene in Deathly Hallows part I.
That scene though was designed to make you think that, but then (if you're going by the movies only) look at their faces at the end of that dance...Hermione just looks so depressed and is basically saying "BUT YOU'RE NOT RON!" through her facial expression.
I've read the books too and have all the movies and I rooted for Harry and Hermione. But Deathly Hallows finalized that for me...that it was just never gonna happen.
But I do agree, in the movies especially, Harry and Hermione had awesome chemistry.