In the world of Teflon, I'm leaning towards Birdsong for the toughest teflon coating. Teflon isn't end all solution though. It does have draw backs.
It is easily scratched relatively speaking. It wears very well though. I have Teflon-S on the frame of my duty weapon. I've been using it here in AZ every day for the past year and no wear has arose. I broke in a Milt SParks holster with it too.
I don't like refinishers who don't reassemble weapons when they're done. The finish changes the tollerances, and sometimes minor fitting is needed.
I don't like the idea of sending a weaapon in 200 parts either. That's a bad mix when UPS or Fedex is involved.
You can run into problems if you have a flash suppressor pinned on, see what that plater/coater intends to do with it. Some want to take them apart.
Birdsong is developing a new coating called Ceramic-T (I don't know if he personally developed the process or if he is just testing it.) As the name implies it is some sort of Ceramic coating. It is supposed to have the lubricant properties of teflon and be more scratch resistant. Last I heard the tollerances were tough to maintain, but this was many months ago.
I've heard good and bad on companies like Bearcoat, Wilson Combat, Robar. Some horror stories.
I've been considering for a while taking about 2 dozen 30 round USGI mags or those steel English mags and having them teflon coated inside and out, including the base plate, put all new springs and anti-tilt followers in them.
A lot of those companies do camo jobs too, if you're into that.
-Steve