I don't think I've ever been content with Superman's hair on film. Something has always been off. And it really shouldn't be this way, because this was one of Henry's best features prior to his casting. He was so perfectly made up for the Superman look it was easy to see him as the character.
I find, personally, that my hair doesn't really have a set style, it's more a subtle side parting, with the fringe/bang messy and falling to one side - i guess similar in style to Ryan Gosling, for want of a better example, but i find that style looks really good when i am dressed smart, like in a shirt or suit, but not so good when i am in casual, sport clothes, and i find i have two styles depending on my dress.
That's how i see Cavill, his supes will only look good with a certain style, in the suit, too messy no good, too neat (ala Routh) and it looks false - his hair as superman is perfect, on top, the sides need to be trimmed, in order to make his face seem more square.
His naturally mesy curls as Clark is a good look, but i think he may lose that, if he cuts the sides short - it's a tough one