To use color as a relative comparison, HC is white and nitrite is black. Those two colors are totally opposite in appearance so it just depends on what you want.

If you like a bright finish that resembles stainless, HC will give you good service.

If your desire is to change the gun's appearance to something more traditional (black) then your choices are limited.

Regardless of type, most of the "black" finishes will show cosmetic wear quicker than HC - all things being equal.

Lastly, there are a lot of folks in the refinishing business out there and they are NOT all created equal. Choose wisely.