I'm not a lubrication or petroleum products expert, but in my experience:
-penetrating oil and "rust buster" products are two different products, with different goals and purposes, and are not interchangeable.
-WD-40, JB-80 and similar products are penetrating oils. They're lightweight petroleum products designed to wick into the threads of fasteners and provide lubrication. The don't necessarily "cut" rust, but can lubricate light- to moderately rusted nuts and bolts enough to ease their removal.
-some penetrating oils, notably WD-40, have water-dispersing qualities and are good for driving water out of electrical components. Don't assume a lubricant will drive water unless it's specified on the can.
-Liquid Wrench, Kroil, PB-Blaster and other products listed as rust-dissolving lubricants chemically dissolve rust. They have lightweight lubricating oil as part of their chemistry, but lubrication is secondary to dissolving rust. If you need to merely lubricate a mechanism, these products will provide lubrication, but a pure lubricant would probably give better long term lubrication and corrosion resistance.
-the secret to busting loose rusted fasteners is more about time than any particular product. Soak, re-soak, and then re-soak a rusty bolt or nut over a period of days, maybe weeks, and the results are often miraculous. Personal preference for one product over another is generally related to patience. Products that work quickly are preferred by impatient people. Like me.
-Repeated tests of various brands and formulations of "rust-cutters" by magazines and private individuals have found that a simple 50/50 blend of automatic transmission fluid (ATF) and acetone generally is as good or better at loosening rusty nuts and bolts as commercial rust-cutting products.