There are some real differences in coatings. All of my carriers are phosphate. I've used hard chromed and NiB in the past. To me, hard chrome, nitride or NP3 are the way to go. NiB stains, reportedly because it actually retains carbon in its surface pores. Microslick wears off. And TiN doesn't seem to offer anything better for the cost. Plus, it's gold.. No thanks.

I'm really not sure why hard chrome seems to have fallen out of favor, even though it's tried and true and holds up extremely well. A couple of years ago, I saw a decades old Colt M16 carrier group that was chromed and had untold thousands of rounds on it. It was slick as snot and the only thing wrong with the carrier was a damaged gas key.

Another excellent option, but hard to find, is ion bond, which is a PVD coating.