I don't think polyester yarn would work well for washcloths, I use whatever brand of cotton is available at Walmart, I've used Peaches and Cream, not sure of other brands. There are lots of cotton yarns available.
No acrylic or poly yarns aren't absorbable. Hobby Lobby's I love this Cotton is a very soft cotton, moreso than the other kitchen cottons, though they soften up a lot. Lion Microspun makes pretty good washcloths.