So many replies here! In my opinion none of them make a case that either -er or -est is more grammatical than the other. Even if this case is not the singular

So many replies here! In my opinion none of them make a case that either -er or -est is more grammatical than the other. Even if this case is not the singular strangest, that does not mean it cannot be a member of ("one of") the singularly strangest group of all the cases. That is, the phrase "one of the strangest cases" would ask the reader to imagine that there is a group of cases, each stranger than any case outside of the group, which contains the case in question. (There would presumably be a group of moderately strange cases and a group of uninteresting cases.) It is a phrase so lacking in precision — appropriate for a subjective statement — that it matters not at all if "stranger" is used in places of "strangest," as the NYT opted to do, except that "stranger" only implies the existence of _one_ group of cases that is less interesting than the one containing the Doig case.