the best diff fluid for me is the one that is changed frequently. Since I have a 4x4 and actually use it for that purpose, it is subject to be contaminated by moisture.
That being said, I just put Redline shockproof lightweight in the manual trans and transfer case, and since I had a pint left over, I dumped that into a half gallon of supertech 80W90, then dumped another quart of ST syn blend 75W90, and had about $15 in both nonlocking axles and a frankenblend of decent oil that will be changed frequently.
I don't overthink something as simple as a nonslip differential. The factory calls for 75W90 in front and 80W90 in rear. ST specs higher than everything in their GL5 gear oils. I wanted something in a gallon jug so I could use my pump, which was more important than the actual oil itself. I too have never seen much gear oil fail in axles.
However, a center viscous diff is an altogether different matter. Go with what the factory specs, or above and you'll be fine.