I use the default theme of GNOME.

  * It is nice, calm and frugal.
  * UI is presented exactly as developers want it.
  * No work for me. Searching for a theme costs time.
  * I don't need hide Linux. Why? GNOME looks better than macOS.

Where theming matters - for me - is the shell and source-code, because readability is crucial and I want it nice. I also care about it on the TTY with screen.