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.
Have you looked at Adobe's site? Tons of great resources to get you going: https://substance3d.adobe.com/tutorials?software=Substance%203D%20Designer As just one example: https://substance3d.adobe.com/tutorials/courses/creating-a-tudor-house-wall