Mobil 1, especially in my AR's. Takes a lot of shooting to burn it all out of the bolt carrier group and it's formulated to deal with carbon.
Also it won't evaporate/dry up like a lot of other dedicated "gun" oils seem to. I can oil up a gun and put it away for a couple years-it will still have lube when I take it back out of storage. I used to use Break Free CLP and after a couple months of non-use, 90% of it will have disappeared. "It leaves an invisible film of protection"-really? I don't believe it unless I can see it.
I mostly use WD40 for cleaning purposes unless I'm trying to remove metal fouling. Sometimes I use the spray carburetor cleaner from Wally world for about 2 bucks a can. And I've used gasoline, diesel fuel, mineral spirits, laquer thinner--lotsa stuff for cleaning depending on what I have on hand and my end purpose.