Neither is good on its own. A dog needs a diet that is balanced in terms of protein, fat and carbs, along with the vitamins and minerals it needs. I think fewer dog foods are beef based, far more are chicken based (or lamb or salmon), for what that's worth.
Both meat proteins are just as good as the other. As long as your dogs isn't sensitive to any particular meat, they should be fine. As far as reported cases of allergies, #1 is beef, #2 is lamb and #3 is chicken. So chicken is 3rd most reported protein allergen and it's on roughly 90% of all dog formulas.
I've fed chicken to my dogs 90% of the time and rotate out to beef, duck/turkey and salmon once every 10 months or so for a bit and go back to chicken. Each type of meat has a different amino acid profile and it is good to change it up anyway. There is a food out there called Dr Harvey's which leaves out oils and meats so you can just add different meats and oils to the food as there's no way to miss out on anything that may lead to deficientcies, y get a much more complete overall diet long term. To much work for me lol so I don't do that but just an example.