I use whatever i have handy. Rem oil is often around as the spray can is convenient, clp is an old standby and it's easy to drop one of the small squeeze bottles in the range bag. I've used motor oil in the past, when i had nothing else, and couldn't tell the difference between it and any high tech expensive lube. I do like Slide glide grease for handgun slides and M1 actions, but again, i think i like the name and the handy little containers it comes in, bearing grease from the local big box seems to work just as well.
I'm easy, if it's slippery and not water based, it's good to go