Wax
The NRA National Firearms Museum uses Renaissance wax on all of their firearms. An article by the museum curator that I found on the web explained that Reaissance wax is chemically inert, which other waxes are not. A ultra thin coat produces a waterproof barrier that resists damage by fingerprints also. They use Renaissance wax on all smooth surfaces, guns, knifes, leather, et cetera.
I've been using Renaissance wax for years. But recently, I started to use it on guns. What I do, is after cleaning the gun, but before I reassemble it, I give it a thin coat of wax. Then I reassemble it, using Militec-1 on the bearing surfaces, and then after reassembly, I coat the gun with a very light layer of oil.
It works like a champ.
I am never without Flitz polish or Renaissance wax. They are among the two best products of their type around.
I have never found a "hard" wax that buffs out as easy as Renaissance wax. A 7 oz can lasts for years. The key to its use is to use as little as possible. It is better to use several coats than one thick one.