I prefer shredded. Its great for both making chicken salad sandwich/wraps and it also works great on club crackers. I once tried a sous vide version with diced/cubed, and the texture was horrible. Had to toss two pounds of chicken salad. In hindsight, i should have tested a small sample before adding the entire two pounds of chicken breast. I could have cooked it a bit longer so i could have at least shredded it. When you think about it, why would you care how much moisture the chicken breast retains when you are adding mayo? The irony is, an extreme moist chicken breast would not absorb mayo, or any liquid for that matter.
Thats what makes tuna salad so good, its dry, it absorbs the mayo which makes the salad.