I've been riding for 13 years now and never understood the difference. I've always stuck to the regular with no copper. Thank you
Ideally the different metals will increase salivation in the horses mouth, leading to better communication. Some horses will have a preference between metals due to the taste. I often use different metals to indicate that we are working on different disciplines.
I know cooper and sweet iron help keep the mouth moist and increase salvation making for a softer mouth. i've always used either of those. I have a sweet iron o-ring snaffle and a cooper D-ring snaffle.
Sweet iron and copper are very similar. They both help the horse salivate which keeps his mouth soft and responsive. Sweet iron is made to rust over time, which is normal and it gives the bit a taste horses like. Stainless steel bits have little taste and keep the horse's mouth dry. Some bits have the stainless steel shanks so they do not rust. My personal preference when I go to purchase a bit is one with either a sweet iron or copper mouth. Hope this helps!