Landscape creation software to use with Unity3D

I am looking for a landscape creation software that works well with Unity3D. Right now I have my eyes on Terragen, GeoControl2 and World Machine 2 but I was wondering if there are others that are worth looking.

If anyone has more experience with the software I mentioned, could you please write few sentences and compare their usage with Unity3D?

// By the looks of it, World Machine 2 seems to be the best with Unity3D so far. A lot of guides on these two and overally everything seems nice.