Compressor crankcase oils have a few determining factors, speed, capacity, splash lube or pressure lube, oil temp cooler controlled and material makeup.
After many years I have seen severe varnishing with Royal, Chemlube and Shell, the least amount of failure and varnishing have been Mobil R 427 and some turbo oils.
I just rec'd Hong, and will upgrade with things like an intercooler and aftercooler also, real inlet filter and get some FLIR images to compare before and after.