What pelleted food brand do you prefer to feed?

I'm looking for something new for Corbi, my keet. He's on Browns Zoo Vital right now, and he's just not doing as well as he used to on it when he was younger.

Any suggestions are welcome! I really can't decide what to buy next?
What should the first ingredients in a pellet diet be? What should the protien/fat/fiber percentages be? Thanks!