The headline does the work when the offer’s core value is best stated in words and the visual merely supports it; the visual does the work when it conveys the product or the feeling faster than any sentence could, and the headline steps back to frame it. The deciding test is simple and specific to the offer: which one communicates the central value more directly, right now, to someone who has never seen this before. Whichever wins that race should lead, and the other should serve it.
The reasoning is that the hero has roughly one second to transmit a single idea, and words and images are not interchangeable carriers of that idea. Some value is propositional, a claim, a promise, a number, a category, and it lands precisely in language while a picture can only gesture at it vaguely. Other value is perceptual, a look, a result, a transformation, an experience, and it lands instantly in an image while words would take a paragraph to approximate and still fall short. Leading with the weaker carrier wastes the one second you have. The failure mode is not choosing the wrong medium in the abstract; it is forcing the medium that cannot carry this particular value to carry it anyway. Notice that this also tells you which element to make secondary, because the supporting medium should pick up exactly what the leading one cannot say: an image leading a perceptual product is best supported by a headline that supplies the promise a photo cannot speak, and a headline leading a propositional offer is best supported by an image that proves the claim is real rather than one that merely decorates.
Take two real heroes. A B2B analytics tool whose value is “see all your marketing spend in one dashboard” needs the headline to lead, because the value is a claim about consolidation that a screenshot alone cannot assert; the dashboard image supports by proving the claim is real, but the words carry the meaning. Now take a furniture brand selling a sofa. No headline communicates the chair’s shape, color, and the warmth of the room as fast as one strong photograph, so the image leads and the headline (“Made to live in, built to last”) supports by adding the promise the picture cannot speak. Same hero slot, opposite division of labor, each decided by which medium delivers the value first.
One case sits outside this: the failure that haunts both directions, the decorative image asked to do a headline’s job, and the self-explanatory product buried behind words. A gorgeous abstract photo paired with a vague headline says nothing, because neither element carries value and the visitor learns only that the page is pretty. Equally, wrapping an obviously visual product in clever copy hides the very thing that would sell it. So leading with the visual is right only when the visual genuinely communicates the value, not merely when it is beautiful, and leading with the headline is right only when words are actually the faster carrier, not when you are uncomfortable trusting an image. The test is communication speed, never aesthetic preference.
When you design the hero, name the single most important thing the visitor must grasp, then ask honestly which medium delivers it faster to a stranger. If the value is a claim, a promise, or a distinction, let the headline carry it and make the image prove it. If the value is a look, a feeling, or a result, let the image carry it and make the headline name the promise it cannot speak. Lead with the faster carrier, and make the other one earn its place by supporting it.