After creating a story with pictures on both Adobe Spark and Sway, it is my opinion that Adobe Spark is the better platform.
Adobe Spark has layouts that are more modern and present the graphics in seamless transitions. It is easier to move the pictures and blocks around in Adobe Spark.
Adobe Spark took me a lot less time to figure out how to use and was much more self explanatory than Sway.
I like that both of the platforms allow you to link videos to your presentation.
I think students would be most successful using Adobe Spark if they were going to tell a story about themselves, presenting a research project or putting together a presentation for a photography unit.