Depends what you're doing, and what your budget is. I have C5 standard, and Vue 6 Infinite.

C5 has more versatility and a better all round toolset e.g.particles, deformations, object arrays that aren't present in Vue, but for landscapes and the Ecosystem technology, Vue is out on its own.

Vue 6 imports Poser (including v7) much better in my experience, including dynamics and morphs, but once imported, it's less flexible than C5. C5 kept losing morphs, and undoing the posing changes I'd made. But rendering results are comparable.

Lighting is generally better quality and more flexible in Vue, but I think C5 volumetric light is better when it comes to shadows.

C5 is more stable, and the interface is a bit more intuitive than Vue.

The Vue renderer shows its quality over C5 when you start doing high quality global illumination and radiosity renders. There's a long thread about this somewhere - I just couldn't get C5 to produce good enough results for daylight architectural renders with everything at best quality, but already I've got better results with V6 and I could pump up values a lot higher e.g. photon counts.

This is just from my experience - hope it helps.

Check out my gallery for some recent PoserVue renders esp "Le Bisou" and "First Contact".

Richard