I think Carrara renders a little more clearly, and the images don't need as much postwork. You can certainly make larger scenes with more people and props in them.

The materials don't convert exactly, but very closely. In particular, you'll almost certainly have to change the values for bump maps. Highlights are handled a little differently, too.

On the other hand, I still really like Poser for setting up scenes, especially doing things like walk cycles for animations.