I am probably not the one to ask. I mean I am no chemist and barely understand much of the chemistry involved.
But, I use sodium nitrate the most just because it is easiest for me to get. That means it is also what I have the most experience with. In my experience much of the problems with using fertilizer grade nitrates can be overcome with really good filtering skills and equipment. Again, orvi can better explain how excess copper can also cause many problems as well. In my mind, it translates to regenerating nitric acid. Making it very hard to remove the nitric/ NOx from AR. Sometimes it is not an issue but others it seems to never stop.
I will use potassium nitrate at times just so I don’t have to make a trip to the store. It seems to actually work better most of the time for me. Even calcium nitrate works well. Each one forms different salts and can change how I handle filtering. A Büchner funnel, good quality and selection of filter papers and a vacuum pump makes a world of difference.
Most of all, experience and time will teach how to see things coming. Start small and gain some experience.