Which pronoun is best when referring to a person: who or that?
For a long time, I’ve labored under that assumption that it’s always who—as in “Courtney is the one who always eats the last donut.” Clearly, that’s better than “Courtney is the one that always eats the last donut.”
But, as Paul Brians explains, my aversion to that “may be praiseworthily sensitive, but it cannot claim the authority of tradition.” He goes on:
In some instances, “that” is clearly preferable to “who”: “She is the only person I know of that prefers whipped cream on her granola.” In the following example, to exchange “that” for “who” would be absurd: “Who was it that said, ‘A woman without a man is like a fish without a bicycle’?”
This is yet another case where your ear should make the final determination. And to train your ear to make the distinction, you need to read. In fact, someone once told me that anyone interested in writing as a vocation should, instead of enrolling in one of the many MFA programs out there, read all the back issues of the New Yorker. The cost of the former? $30,000 at your average public university. The latter? A buck a week for access to their archives.
