either will work in lazersteves directions, but from my experience, potassium nitrate gives a better quality and yield.
Butchers method is different. it uses sodium nitrate and sulfuric acid to digest (or dissolve) gold plated pins producing the NO2 fumes that you have to capture in water (or hydrogen peroxide) to make the acid. it makes a cleaner acid that works better with silver. plus you get clean gold foils from your pins when your done. its a little more work to it and you will need two hotplates. one to heat the solution and one to heat water. if you do Butchers method, follow his instructions exactly as he has them written because you will be dealing with hot acids and very nasty fumes. either way is dangerous enough so try and be as safe as you can be. wear gloves and eye protection.