When comparing elementary vs Papirus, the Slant community recommends Papirus for most people. In the question“What are the best icon sets for Unix-like desktops?” Papirus is ranked 1st while elementary is ranked 8th. The most important reason people chose Papirus is:
All icons look pleasing, especially with the Arc theme.
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Pros
Pro Good contrast
Icons have a dark border around plus a subtle shadow at the bottom and hilight on the top to improve the contrast with the background.
Pro Sharp, flat, and fresh
All icons look pleasing, especially with the Arc theme.
Pro Familiar
Used on Lubuntu and BunsenLabs, for example.
Pro Active development
Cons
Con Under GNU GPL3
This limits the use elsewhere.
Con Contrast issues / No border around icons
It makes the the fast and makes it simple to add more icons(since you can simply scale them) however the contrast is lost in some situations.
Con No Ideas
It just copies the icon-syle from a different system.
Con Just another material style copy
Con Lacks icon for backintime
Backintime tray icon doesn't display on the panel because Papirus lacks the icon.