Sometimes it is just what works well for the individual, the guns they use, and the way they use them. I bet if I were in Arizona instead of Tennessee I might change my favorite gun oils and cleaners and protectants for storage.
Most gun kits I bought as a kid contained a nitro solvent for cleaning and a clear oil for lubricant and a gun grease in a tube that looked like cosmoline.
I have been preferring Break Free CLP (cleaner lubricant protectant) since it was recommended by a family friend who was in 82nd Airborne starting back in the 1980s. If there is room in the bag for one bottle, Break Free goes in. My experience is it fills the lubricant role better than cleaner or long term protectant. You can find better products for the three roles of liquids in gun maintenance, and specialty items within the three roles.
I tend to buy large bottles Hoppes#9 and Break Free CLP, refilling smaller bottles for the home cleaning kit and range bags.
I have also had 10W nondetergent motor oil recommended to me as a lubricant; as I recall it seemed to be as effective the more expensive product-specific clear gun oils. For that I have use Outers and Remington brand gun oils, probably the only reason is the convenient bottle size.
I have not used ATF and have no reason or rumor to doubt it works too. It appears to be a fine alternative.
On "running wet or dry", I clean AK or AR wiping after cleaning with solvent, using a lightly oiled cloth to leave a bare sheen of oil on parts, then use Q-tip or pipe cleaner to oil all metal-to-metal contact surfaces (which are fewer on the AK). I tend to leave surfaces directly exposed to hot gas dry not wet.
Before I duck for cover, WD40 and 3-in-1 can be used on disassembled parts as cheap cleaners if they are wiped off before re-assembly; over time (storage) WD40 solvent evaporates leaving behind a wax (that's how water displacement works), and 3-in-1 appears to both evaporate somewhat and oxidize into a varnish.
