Images, GIFs or Video: Which Perform Best on Instagram?
This article is much more nuanced than most. Rather than just report analytics based on a zillion posts, the author walks you through the different results from organic and paid posts as well as well as some interesting insights into Instagram's algorithms.
If you want the simple answer, you'll find it in the final paragraph:
"There you have it — images perform better for both organic and paid Instagram content, as well as in Instagram Stories. If you choose to post on your Instagram Stories, the more natural your content, the better. These findings aren’t to say video and GIF content doesn’t succeed, however. Implement these trends alongside your audience analytics to produce the most impactful Instagram content."