3D Vim, why don't you download the demo of Vue5 Infinte and see for yourslef if it suits your needs?

Vue is not a modeller, you can create basic shapes with primites, and do boolean operations. You can also create organic shapes with metablobs ( = metaballs, but with more possibilities)

Vue comes with vegetation, and terragen can't do vegetation right now.

Vue imports all major 3d file formats, and TG doesn't at the moment.

Vue has global illumination, radiosity and image based lighting. TG doesn't.

TG atmospheric effects are better than Vue5, but with Vue6 around the corner, it's all gonna change.

TG's renderer is faster ( well it's easy to be, because there is no imported geometry to compute, and no advanced lighting models.)

TG'renderer is the most photorealistic you can get for now. This is going to change too imho with Vue6.

Terragen (TG) 2 has been postponed for about 2 years now, while Vue has dramatically improved in all natural environnement rendering aspects over the same period.

TG is free for non commercial use, Vue Infinite is expensive.