Up until now, I was never sure. I had an opinion, but not one deeply rooted, as I have not experienced the updated game firsthand. Now I am sure -- not because I have played the updated game, but because of the official Nintendo video below -- and I am sad that I have to say the following: The Wind Waker looks better than The Wind Waker HD. I prefer the aesthetics of the original game, and I would have loved an upgrade without the updated light effects, and without the new brighter and more realistic sky. Much of the visual charm has been taken out. I might actually skip TWWHD, and play it again on GameCube instead.
Comparison video: