NJtuna;
Welcome to the forum.
I also used white sugar in this recipe. Brown sugar will give it a different taste, and during storage it will harden in the rub (unless you dry it in the oven first).
Unless I'm looking for that brown sugar flavor, I now use white sugar. I thought brown sugar was less process then white, but a year ago I learned how commercial brown sugar is made. They refine it to white sugar, then add the molasses back into it.