I wish to get some advise for 1 MASTER and 9 SLAVES PC for performing rendering over network. I need to know if I CPU versus GPU rendering is faster? If yes then I will buy more powerful CPU and use a low-end graphic card.
It really depends on your scene. At the Blender Institute we render mostly on CPUs; when a GPU runs out of memory it'll crash, and when a CPU runs out of memory it'll swap. Things will get slow, but at least the render will finish at some point. Of course it also helps that we have a few very nice servers with CPU 40-80 cores each. If the RAM required to render the scene fits the GPU memory, things should be fine and it really depends on what kind of hardware you fit exactly.
On the flip side, with Blender 2.79a now supporting rendering scenes larger than GPU memory allows as of 2018, I would say GPU rendering is a much more economic strategy for most small productions.
Price wise it's actually quite similar, a $300 Ryzen 7 CPU will perform similarly to a $300 GPU from either AMD or Nvidia. But, the benefit of GPU is that it scales up wonderfully, you can easily buy a motherboard that supports 4 GPUs, which gives you nearly 4x the speedup, whereas dual-socket or quad socket systems are quite pricy.