Terrain Building Tools Preference

Looking around - we have quite a few tools available to us. Of particular interest to me I have found:

Gaea and World Machine to generate height maps (some very nice terrain made from these)

but I also note Gaia Pro and GeNa Pro.

Can I get some input on these systems and how you are going about building your terrain and what you prefer? I know we also have Unity's terrain tools out of the box, and I use those for sandboxing ideas but I don't think I have the ability or patience to generate nice looking terrain manually like that.