What is the best recommended set up? NAS, HTPC ??

I have a big library of movies, music and videos on a PC, which I have shared on the network. The media files stream to ATV2 and another HTPC connected to a TV. I am happy with the performance but I have recently been thinking about decomissioning my file server and using a NAS instead to house my library.

But I am wondering if that would be a better solution. How is a PC sharing files over the network different from a NAS or unRAID server? Is there any other type of setup that can provide better performance and perhaps lower energy consumption?

Thanks for your input.