the finishes are totally different although I think either one would look good. A molycoat/duracoat type finish will certainly have a lot better corrosion resistance than blueing.
If you really want blued finish you can always find a special refinisher that does blueing, such as Accurate Plating and Weaponry
www.apwcogan.comThe problem is that a lot of times the parts get over polished, meaning they remove too much material during surface preparation and so the parts/edges may look rounded after it's done, and I personally don't like that. Some refinishers do it and some are more careful.
I think a better alternative to the Molycoating/Duracoat and blueing would be IGF's environtech black finish, it's very corrosion resistent and very thin (the molycoat/duracoat, which are really thick in comparison), has a nice satiny texture, almost like matte blue but slightly more reflective. Also, the Environtech finish wears evenly, where as moly type coating would chip instead.
Here you can compare the Environtech finish(SA M7 Classic) to blued finish (Polytech Legend)
Also, if you don't mind me asking, you're in CA right? How did you manage to get Firing Line receivers? Is it considered a non-listed receiver?