Here are a couple of good articles from the Dogfoodadvisor website:
Dog Food Allergies | Frequently Asked Questions Hypoallergenic Dog Foods
They give a list of food ingredients that dogs are most commonly allergic to, as well as a list of dog food brands that are hypoallergenic. That said, almost anything is better than Beneful, so if were me, I'd get a small bag of the Blue Buffalo first to see if it helps, and if not, try some of the hypoallergenic brands.