The important thing is that the feed is fresh and meets the minimum nutritional levels for adequate performance at a price you are willing to pay.
"Corn Free", "Soy Free", and "Organic" are largely marketing, they have little if anything to do with the adequacy of the feed.
Not to stir the pot, but the research on the health effects of soy (see
the CA Teacher's Study, the largest, longest duration, human food trial in history) is "complicated". Its clearly of benefit to some - and clearly a risk to others with certain health conditions. Plenty of people who know just enough to show their ignorance will claim, "but phytoestrogens!". Yes, Soy contains phytoestrogens in significant amount. So does flax, sesame, wheat, barley, alfala, lentils, beans, and in more moderate amounts, rice, and a number of fruits and veggies. But only soy gets the bad rap, almost as if its reputation has nothing to do with its nutrition.
Otoh, Soy is one of the only essentially complete proteins in the plant world - Soy meal is among a bare few of low fat, high protein, reasonable cost ingredients for animal feed (such as chickens) which has a high methionine level. Met is the #1 most critical limiting amino acid in a chicken's diet, and its difficult to find elsewhere without using aimal ingredients. So difficult, in fact, that synthetic methionine (appears as DL-Methionine on the feed label) can be added to feed while maintaining its "Organic" designation.