Ok, here's how I make terrain.
First I create a brush with a size of the area I want to create and texture it with BEVEL to decrease the amount of clipnodes: Then I clip it into multiple triangular prisms: After that I enter VM and start dragging verticies vertically: When I'm fine with the results I start to texture it. First I apply the texture I need to the ground: Then I select the face I applied the texture to and press Shift+F6: And I start left-clicking on the ground faces applying the texture to them: After that I do the same with the cliffs: I scale up the cliff texture a bit to get better results: Then I again use Shift+F6 to apply the cliff texture: There's a screenie of what you can make using this method: