I have had good luck feeding a Chicken and Rice food that is packaged here for a local Farm supply. It's equivalent to the other premium foods such as Eukanuba.
It's not corn based, which to me is one sign of a quality feed. Corn is a filler, and in my experience, there isn't a digestive system in the world that can actually digest it. So - all the corn just ends up going out the dog remarkably unchanged from how it went in.
The other thing I look for in a feed is that it contains no unidentified "animal" as the meat source, as that almost always indicates horse meat (among other things at the rendering plant) and I refuse to support that.
One thing I've also heard about "crude protein" sources, and this could be urban legend, is that they're not too picky about what constitutes "protein". For instance, say a turkey or chicken has a huge benign (or even malignant) tumor in its body-- that tumor ends up included in the protein source. Pretty ick, and possibly even dangerous, if you ask me.