It depends on the scene that I'm trying to render,

A single figure that I plan on being able to copy/paste to any background would usually be 128.

A complex scene could be 64, 32 or even 8.  If I have to get to 8 to render something, that's when I usually hide things and render bits and pieces and reassemble the scene in Paint Shop Pro using blend mode "Difference" to make sure that I have  the various layers of things lining up properly.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi