I have seen in Wikipedia that different quantization methods exist (see Wiki article with name "Quantization"). Moreover, Wikipedia stated that there is more than one way to quantize a classical theory. Why? Why quantization is not unique?
If you hear lectures about quantum theory, you will learn the canonical (commutator relation) quantization and the Path integral method. You will learn that canonical method and Path integral method are equivalent.
Now there also exists a quantization with the Moyal $\star$ product and phase space; this method is also equivalent to the methods I have mentioned previously.
Main question: Which quantization method is completely different to the most convenient one like commutator relations? I am thinking about things like the spin network state quantization that is used in Loop quantum gravity. Can spin networks be used to quantize well-understood theories like quantum chromodynamics also?
Answers would be greatly appreciated.