You can use either, depending on what your specific needs are.
You might also want to look at trilinear texture mapping, which is a good way to get landscapes to look better when they get steeper.
Also, you might want to get the Brushify shader on the marketplace, and open it up and look at how it’s implemented. It does a lot of smart things to make landscapes look good when painted. Any of the Brushify packs will contain the full shader; the main difference between the packs is the sample levels and additional decoration meshes that come with it. The Brushify Environment Shader pack is the cheapest way to get the landscape shader, without any additional assets: Brushify - Environment Shaders Pack in Materials - UE Marketplace