This might sound like a joke, but it's the honest truth - in my experience, whether image or video, we get the best reach if it involves snow. But video that involves snow have been our big winners on Faceboo (this is for a resort in a mountainous area).
What sort of content (subject or industry) are you putting out there? Perhaps it has something to do with that. As I'm in tourism, anything that immerses people in the destination does better (gets shared, liked and tagged a lot more) and video is best in that situation. But for some products or services, I would imagine video would be less relevant... web hosting for example.