I use what the manufacturers recommend, I just don’t usually buy it in their labelled bottles- I can’t remember off the top of my head but I think the current Fox oils are torco and rockshox is maxima (fox used to have one that was a silkolene but I think they swapped). A litre of rockshox 15W is £17 at Tredz, a litre of what seems to be the same stuff branded maxima with a black bottle instead of red is £7.
OTOH, the volumes you use are pretty small so if you want an easy life and presence of mind, it’s not a terrible option to get the expensive “own brand”
Depends a lot on if you want the weights to be right, can’t find the chart that avalanche had but the weight variation over oils all with the same lable was huge.
Here we go:
http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid