"Educative" vs "insightful"

"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).

You can use words like educational, educative, informative or instructive to suggest that the article teaches something to the reader.

On the other hand, insightful suggests to me that the article provides a particularly thorough or fresh perspective on its topics.

I would not say these words are precisely synonymous, so either word could be appropriate depending on what the author is trying to say about the article.

Imagine an article about the life of Richard Nixon. If I said I found it educative then I'm saying I learnt something through reading the article. Perhaps there were some interesting facts that I wasn't previously aware of. The word informative might be more commonly used. To say that I found the article insightful implies a deeper examination of the subject, that the author has gone beyond the bald facts of Nixon's life to discuss, say, his politics and how they relate to his upbringing, and so on.