Best flour for making focaccia?

I use King Arthur bread flour for focaccia. I like lots of chew in my focaccia. All-purpose flour would work, though.

Use bread flour; its stronger gluten allows for more stretch, resulting in more and larger air holes, which you want in focaccia. I usually buy King Arthur, but any national brand of bread flour that hasn't been on the shelf too long should be fine. I bake artisanal and sandwich breads of all kinds, at least several times a week, and have been for quite a while (as in, decades). In my experience, using bread flour does make a difference with yeast doughs. ;o)

I'm sure your King Arthur is fine. I've been successfully baking bread for decades, and have never used any of the specialty "bread flours." I first started using King Arthur flour when I moved to the East Coast, and I think they have fine products.

I also use all purpose flour for focaccia. It's such a light and fluffy bread I think bread flour would be too dense.

I use King Arthur all purpose with great results. I also use King Arthur white whole wheat as a part of the flour amount in focaccia recipes.