I think that a younger link is better. I think that one of the things that makes Link, Link is his purity, and that just conveys better through somebody younger. I don't really think you can have an adult toon link, so I think he fits under the category of a young Link.
Depends on the story. Young Link was ideal for Majora's Mask, a game about the preservation of innocence above all else. On the other hand, a younger Link wouldn't have worked at all for a darker game like Twilight Princess.
Personally, I like Adult Link, although I love the cell shaded style of Toon Link. So Skyward Sword Link was my favorite, aesthetically.
I prefer an older, teenage Link. Even for Majora's Mask, I didn't like the fact that Link was a child. It seems a bit unrealistic to me, a child being capable of all of that. And while, yes, I understand LoZ is definitely not a realistic game, there is more of a sense of adventure to it when Link is older. It makes it seem more possible.