A very low poly out from zbrush is my personal favourite. The reason being that we can polypaint in zbrush and mudbox, so the texturing isnt an issue. Painting in Unity onto terrain STILL ends with stretched UVs which are plain ugly and totally avoidable using polypaint and UVing properly. The landscape tools using heightmapping takes more time than just zremeshing a zbrush model, and slopes and caves dont work with them (as theyre just Y axis extrusions essentially). Basically landscape isnt worth using.
And it flips the image on the way into unity for some reason...
It may be faster for vast areas of terrain, but we wont be using vast areas of terrain for the moment. So for now... Its all classic geometry for us...