It's easy... Harry needs Ron. Harry is the straight-man to Ron's cut-up and without Ron, he's lost. Especially when it comes to acting quality. Ratcliffe stinks and Grint is by far the best actor of the Hogwarts Students. It's not even close. He's funny, and that's not easy. He's also charming and has great timing. Hermione needs him equally as much - she needs a foil for romantic frustrations - it's the only dimension she has. Watson is almost as bad an actress as Ratcliffe, however, here cuteness makes up for most of it.
Thoughts?