It’s hard to say which one would do better without comparing one to the other. A great quality image could be more engaging than a mediocre video. An annoying video can do more harm than good as well. Or one that is not align with the brand… like an overly funny or creative video when people just want to be told straight what you are selling, who it is for, and where to go next if they’re interested.
The thing that I will say that makes video better than images is the ability to create custom audiences in Facebook for people who watch a certain amount of the video. Especially if you add in a lot of filtration elements in the video. I have a client that has a video on one of his landing pages (same strategy could work on an ad) and around the 1 minute mark, he specifically states something like “If you are currently NOT x, y, and z then this video may not be for you”