I think food choice is one of the most important issues to lock down for any dog... unfortunately, it's also one with the most variables.
I ended up using Fromm's Surf & Turf grain free food. Fromm also has a Beef grain free, but Arwen got hives from it. So, it's not just the gain issue, but also the protein sources that can cause reactions.
What I did was find a small high end food store in my area, and got some samples and some small bags of food to try. I love the local store I found, the owners call out Arwen's name as soon as we open the door - they love dogs (and last time we were in, she even laid on the floor to give Arwen some love!), and focus on what is best for them - they won't even carry dog food that is not good for your dog.
Take a look at the dog food rating here on the site (under the Articles tab at the top of the page) - it's a great place to start. Just remember you may go through a few foods until you nail down the one that is not only good for your Bully, but also relieves most, if not all, of his issues.