Is using Custom Shading model better than using Postprocess?

I’m trying to make a Toon Shader on Unreal Engine.
Creating using Postprocess Material was successful. However, I suddenly thought it would be more efficient to add a Toon Shading Model to the Material Editor using Custom Shading model.
Which do you think is more efficient, using postprocess materials, using the Lit shading model, or using the Custom Shading Model?