Ronaldo's become a very clutch goal threat in important games for both Portugal and Real, so he's a definite possibility depending on how far they go. Messi could be head and shoulders above anyone, he just has to reclaim the "edge" he had up until 11-12. That's not to say that he's in some sort of massive decline now, just that he's no longer THAT far ahead of everyone else and his ability would allow him to perform much better than what he is now. Higuain and anyone from Germany would be up there as well.
It really depends on which team does well though.