From personal experience, what have you found to be the best dog food for Great Danes?

I have 6 beautiful Danes: Ray, Georgia, Louis (harlequin), Bijoux, Duke (blue), and Billie (black) . However, lately, all of their coats have lost lustre and they don't have as much energy as they used to. Whenever we go outside for our usual run, they just stay by my side. I have been feeding them Eagle Pack because a friend of mine suggested it to me. I'm really frustrated! I don't wnat my Danes to get really ill, or even die, from poor nutrition.