Hard to choose I like both equally. I will say though I'd like to maybe see another Zelda game where we have both. Except this time he doesn't go back and fourth through time instead he just goes into his adulthood. That would be interesting.
Both of them obviously have their place. However, the games I enjoy most nowadays (and like many of you, my interests are constantly changing) involve an adult Link. But choosing only one would be impossible. They both fit perfectly in the environments they're put.
Personally I believe that it depends on the game. In every Zelda game the world is designed for the age of Link. You can't see Young Link doin' all that fangled-hoowassit that Link does in TP! And you can't have Link doin' childish things like picking up farting pigs, or playin' hide n' seek with pre-schoolers!