I prefer pima cotton because of ethical reasons. Modal, a form of man-made cellulose fiber, is often manufactured with harsh chemicals which are often times dumped into the environment. I know, just what you wanted to hear....another chemical slamming. That's just how I feel about it. But otherwise both fabrics are very soft and feel good on your skin. Modal does not shrink as much as pima and since modal has a more silky finish, it tends to exhibit less pilling than pima.