I use Vue 6 Infinite & I love it, one of the best purchases I've made. I haven't tried Carrara but I've heard it's good.
Regarding Vue, if you want more life in your renders this is the way to go. Global Illumination & Global Radiosity can give you realistic light which Poser can't, the render engine is very good. Poser imports in the main go by without a hitch. Some people have the odd issue, but in general it's fine. The only thing I need to work on regarding Poser imports are the materials to get them looking better, ie highlights, bump etc.
Vue is great for indoor & outdoor work due to it's great light implementation.