I often read complaints about less than optimal anti-aliasing on curves in Rhino 8. For some reason, there is no difference between 2x, 4x and 8x anti-aliasing even in the latest Rhino 8.3 release. Seems like a bug to me.
However, you can use a temporary solution to this, which makes the aliasing appear less aggressive to the eyes. There is a hidden command called testWireThicknessScale which lets you control the thickness of the curves, isocurves and surface edges. A value of 1,5 gives a nice result, but you can try any other value according to your liking.
I recommend to place the following command in Rhino Options > General:
testWireThicknessScale Enabled=On Scale=1.5 Enter
