Differences are; That the original Noct is f/1.2 with an aspherical hand ground front lens element and build quality is very high.We have a thread where it is chipped with CPU, there you clearly see how well made it is.The new Noct is another way of designing and engineering a lens altogether, it's from another vintage,,, many years apart - Manual focus!
The new Noct is quite popular among the photographers that can see the amazing tonal transitions and Bokeh and are not looking for sharp corner perfection
It's plenty sharp for portraits etc. and over all a wonderful lens.
There is not the matter of a choice between theses two lenses, get both
they are really different if you look closer!