i use yotsoyba b because it's easy to look at and so far it doesn't break anything
every other theme in my experience either breaks something (dark theme makes many text elements invisible on my screen) or breaks text highlighting (i would use the FNAC theme, but it makes selected text in my browser become invisible for some reason and its just crappy to deal with) or is an eyesore to look at because of contrast issues or something else (somehow, i doubt browsing the shlog with the cacaborea theme on for more than 10 minutes would be a pleasant experience)