I've seen (and used) a variety of lubricants on all sorts of guns, including ARs. My last AR was lubed exclusively with LSA, and it did fine. In the Air Force, I've used both LSA and CLP. Here and elsewhere I've seen discussions of using everything from exotic synthetics and other, special purpose lubricants to single-grade motor oil.
Whatever happened to good old "light machine oil?" This is the same sort of stuff that the Army called "PL Special" in the Garand days, and works out to the same stuff you use on good fishing reels and sewing machines, and the stuff the CMP folks use on the Garands they sell.
It's plentiful, cheap, and built for fine tolerance equipment and high speed, high temperature uses. I got a quart of the stuff when I bought my office shredder, and noticed immediately that it lacks the detergents and additives found in motor oil. It is also very light and easy to apply, making it a breeze to use.
Is there any problem with this stuff, or is it just not "the best" lubricant?
CLP - clean, lubricant, protect
Light machine oil = lubricant
CLP does more than just lubricate. I've seen too many guns screwed up that are easily fixed with a good clean and clp lube job.