If you see both OBJ and TGO versions of an object, choose the TGO. That is probably going to have the shaders set up properly for Terragen by whoever made it. If you load the OBJ, it might load all the textures and set up the shaders properly, but not always.
However, if you chose OBJ and made adjustments to render correctly in Terragen, don't need to resave as TGO. Your project file (.TGD) will remember all the changes you made to the OBJ for that project. You can even copy the OBJ reader node into other projects; no TGO necessary. But TGO is a useful way to share objects.
Matt
