As they go, a good a synthetic/natural fibre that keeps the cost low and benefits from the best of their individual properties: hardwearing, long lasting, soft to touch, non-creasing, absorbent while quickly releasing moisture.
Cotton will always feel better and will look better for longer, but if you have masses of children or a household where the laundry is constantly on the go and have no objections to synthetic fibres, or the mechanised cotton production industry, polyester cotton is a reasonable alternative to cotton, especially for bedding and seat cushion covers.