I've got superficial experience with about half a dozen 3d programs, and personally I found Blender the easiest to learn and use. Making terrain manually is pretty easy, especially in the sculpt mode with some noise brushes. I believe there are also plugins which can generate terrain automatically. However, I'm not sure how good it is at handling larger projects, maybe someone else knows?
There's a tutorial on how to move files between 3dmax and Blender here.
Hope it works out, and keep us updated