When comparing Arc vs OneStepBack, the Slant community recommends Arc for most people. In the question“What are the best gtk3 themes?” Arc is ranked 2nd while OneStepBack is ranked 5th.
Ranked in these QuestionsQuestion Ranking
Pro Customizable to dark or light themes
Pro Has both GTK2 and GTK 3 support
Users will be able to match their gtk2 and gtk3 themes easily due to Arc supporting both.
Pro Available firefox and chromium themes
There are matching themes for Firefox and Chromium for those that want to have a fully matched looking environment.
Pro Supports gnome-shell
Pro Really clean and nice-looking
Pro Easy on the eyes
The color combination has been carefully engineered exactly for the purpose of making people comfortable, while staring at the monitor for a prolonged period of time.
Pro Allows you to focus on what's needed
The design is extremely basic - using just 1 color accompanied by 3 shades of grey, OneStepBack manages to be a very functional theme without adding any flashy.
Con Bleak font colors that cause eye strain
The font color in Arc and Arc-Darker is not black, but lightgray
after prolonged usage, it becomes apparent that this font color, combined with white backgrounds causes too much eye strain
Con Has some contrast issues
The theme is a low contrast theme so it really depends on the screen brightness if you see borders or the text, some elements don't even have borders - this makes the theme barely usable for portable devices.
Con Funky arrow button colors in FireFox
The developer is currently aware of this issue, however the fix can't be made until FireFox has an update.