Users perceive and use Instagram Stories and Feed in different ways, and are driven to both formats for different reasons.
At the current growth rate for Stories, they are set to overtake the traditional newsfeed for sharing in the future.
Instagram feed ads with additional text can still outperform Stories for cost per conversion.
But, when the ad text is removed, Stories actually have a slightly better CPA by 6%.
A stories advert generated more interest (seen in website traffic), but due to the limitations of the format, they were unable to convey enough info in the ad itself so to have a lower conversion rate.
The choice between Stories and News Feed ads depends on the offer you are presenting.
A complex product such as ebook is hard to explain in a 15-second video, however, a simple offer like "half-priced [insert product here] if you show this coupon on Friday" could see significant results with the Stories format.
Stories require more creative resources, especially if you want to fit in with the look and feel of organic Stories posts which are usually pretty informal.