Bluing is very pretty and if well cared for will last quite some time. As far as it's protective qualities, it leaves much to be desired. There are only two things that will rust faster than a blued gun: bare metal and anything with that finish that Remington 700 SPS rifles have on them. I don't know what that stuff is but you can look at it the wrong way and it will rust. For guns that will see real world use (concealed/duty carry, large amounts of hunting in inclement weather, etc.), bluing is a poor choice. For range toys and safe queens bluing is fine if you will maintain it well.
I've noticed a definite shift away from bluing on new firearms in the last couple of years, particularly on "work" guns. I saw a new Marlin 336 the other day, for example, stocked in laminate and sporting a Duracoat type finish. Not as pretty as an old one, but definitely more durable.
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