Description for dither modes would be helpful or even better link to the source with all modes listed and example gif next to them.
Here's what I found after testing all of them (ffmpeg 4.3.1):
The best quality overall will give you TURBO mode but the file size is significantly larger. You will preserve the most information and it resembles your composition the most.
If you're looking for small size:
Dither set to none is the best but still not as good as TURBO mode
Dithers:
When it comes to details preservation o4x4 wins over h4x4a in my case
o8x8 more artifacts (every surface will get some gradient)
hbx6a, h8x8a - blocky effect
c5x5b, c5x5w - grid effect
c6x6b, c6x6w - combination of blocky and grid effect