If you can't get realistic human renders out of Carrara you're not doing it right.
There are 4 things that will determine the level of realism;

The mesh
The textures
The lighting
The render settings

The only thing that may differ in any of those between Carrara and Lightwave would be the Render settings.

For any advanced shader techniques there are inexpensive plug-ins for Carrara like deeper and Shader Ops.
Other than that, it's all there.
You just need to know how to use it.

Carrara's biggest drawback is the lack of up to date tutorials and tutorials that go over anything but the basics.