Well, something like Forest Pro from iToo, so it has models library which I can then scatter around my scene. It would be great if it has grass/flowers/trees - all in one package.
I think that Forest might be the best choice since it has Corona materials on the models already.
I find better to use a specific plugin to create vegetation like GrowFX and use Forest Pack to scatter the vegetation. You get better model quality if that is something you are looking for. Laubwerk also have good trees.
for me scattering: forest Pack Pro
for me vegetation: models from Evermotion, mostly it will do. But if the client request something specifik I Use Grow Fx
Meanwhile, anyone tried using Speed Tree? I am reading at the moment about it, it is quite pricey but they do have some Speed Tree Architect version for 400$ that seems decent, and the trees look wonderful. You can even draw your own trees with a tablet using pre-built textures and UV maps.
Not sure how would that work with Corona in the end though, probably export to max/vray then use the material converter script.