"Educative" is a synonym for "pedagogical", or "didactic", which means it teaches other people something significant, interesting, or otherwise important knowledge.
"Insightful" is an adjective which says that someone's work has brought light, new understanding, or a new perspective to the topic at hand; it may not actually teach anyone anything, though, because it may already be re-hashing established knowledge (as when a student prepares a term paper for a teacher), or it may simply be re-introducing knowledge or a topic from a new, hitherto unexplored angle (as often happens with poetry, good literary and arts criticism, and so on).
So the answer is: this depends on what you want to emphasize. Do you want to say people can learn a lot from this article? Or do you want to say that the article just gives people a new perspective on something?
Obviously, a well-written article can be both educative and insightful; the two ideas do share some overlap, and in some instances can be used interchangeably. One must make sure, however, that both meanings are intended, because not all educative works are insightful (think a basic reader for first-graders), and not all insightful works are educative (think of a comedic piece by Richard Pryor, or Bill Hicks).