I like Carrara 6 Pro, DAZ Studio, and Poser 7 - I certainly think that Carrara has advantages over Poser in terms of lighting and rendering.  I also think that dynamic hair looks better in Carrara.  

But Poser has definite advantages in terms of creating and controlling more diverse shader materials due to the node based set up.  As a result, I think that skin still looks a little more realistic in Poser than Carrara, particularly with Bagginsbill and the Real Skin Shaders.  I also think that it's easier to set the filter value on textures in Poser than Carrara to make them look less blurry.  Poser also has python support which allows for a wider range of scripting and plugins.  

DAZ Studio seems to handle textures better than either Poser or Carrara, but with much less shader options than either of them.  The lighting and rendering in DAZ Studio are excellent.  Good skin effects are possible in DAZ Studio, but mainly due to the lighting rather than the materials.  Personally, I wish that both Carrara and DAZ Studio had node-based shaders like Poser.

Both DAZ Studio and Carrara have support for figure scaling for conformed figures whereas Poser doesn't.  This is particularly noticable for Apollo users who can apply ADS settings to the figure and then have the Epic clothing assume the same scaling and morphs upon conforming.

These are just my observations/opinions...