I use mainly L3DT, its okay for 3DGS and Esenthel too, and probably for any engine that can import heightmap and textures
Another free tool (with hmp export) I use rarely is PnP Terrain Creator.
Unity pricing is not okay for me, free has no enough features, Pro is too expensive, but its terrain system is cool, and gave me a lot of ideas for the terrain manipulation part of my editor.
The other engines you mentioned are not for my taste or capabilities.