I'd like to add a bit to what ZURI said because I think terrain is an important topic. A terrain mesh always works out better when it contains mesh loops. Just think of a topographical map, but with all the concentric circles connected to the adjacent circles by faces. I've found the mesh to be much more workable with the organization of mesh, rather than having a subdivided plane with the heightmap applied. All that said, sometimes a grid-like mesh is all you need for a terrain.
I'd say that everything depends on how important the mesh is in your age. If a terrain is not scenery (you are able to walk on it) it should be modeled by hand. This is because it is much easier to texture custom models.
Keep in mind that this is just advice, if you have a method that's producing good results, stick with by all means.
Currently getting some ink on my hands over at the Guild Of Ink-Makers (PyPRP2).