Im making a bunch of broken buildings for a war scene where the materials blend between bricks/plaster where its broken. Ideally I would use vertex paint to make buildings look different, but that would involve me vert painting a bunch of buildings, which is fine but a little time consuming... but I would get more variety…
Both. You'll probably use vert paint, being cheap and effective way to blend materials, and probably masks, even if it's just a basic noise and gradient material function to break up vertex paint blending or height lerp from a height imput for example. Also don't forget decals on top of what ever solution you use.