This is one of those questions that is almost impossible to answer. EVERY dog is different when it comes to allergies. However, there is a food rating chart here on EBN to guide you along the way http://www.englishbulldognews.com/co...g-Food-Ratings
A lot of work has gone into this and its a good place to start. Some bullies are very food allergic and others, not so much. Whatever you choose, make the change slowly and monitor your bullies intake of other things closely as well. Doesn't do any good to get them the best food and then give them junk for treats.
Generally tho, Purina is not looked on favorably by a lot of people.