It’s unclear to me why NVIDIA states that Nsight is a replacement for FX Composer. It’s does have editing capability, but not visualization. While that tool is absolutely fantastic at profiling and debugging, it’s no more an authoring/visualization tool than any text editor.
Nsight’s editing capability allows you to modify a shader while debugging — which is extremely cool. But I know of no visualization features within Nsight.
If you’re a Windows 8.1 user, the latest version of FX Composer won’t function. However, a previous version does.
The Visual Studio 2013 Shader Designer is quite different from NVIDIA FX Composer and has (to my knowledge) no similarity to anything within NVIDIA Nsight. The VS 2013 Shader Designer is a visual editor that’s graph-node based. You make connections between nodes to control the shader’s output. The end result is generated HLSL.
Maybe you have a look at ShaderTool. It is a new node based shader editor but with additional HLSL and GLSL coder editor functionality. You can just code shaders as in FX Composer but also use the node system to build up your own rendering pipeline.