im using terragen, doing assets in softimage/gaea then importing it into Terragen, i've bought a license and started using it and got blown away by the quality of the renders, it looks so real. Everything is procedural, the quality of the Atmosphere and the clouds in general is probably te best on the market.
But its a bit like houdini, lots of nodes, proceduralism and math, but i decided to study it because if you are in for environment art (which i love) i think there is nothing that comes closer to it. I'll post some other stuff im doing, but im still a total newb at it
p.s there is a discount on terragen creative version for like 200$ so i got myself a copy