Polari vs The Lounge
When comparing Polari vs The Lounge, the Slant community recommends The Lounge for most people. In the question“What are the best IRC clients for UNIX-like systems?” The Lounge is ranked 10th while Polari is ranked 12th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Great UI
The CSD-based UI is great to look at. No screen space goes entirely wasted and is presented neatly.

Pro Easy to use
Polari is very straight forward to use.

Pro GNOME-Integration
Polari integrates nice with GNOME, on a visual and technical level. It uses GNOME online accounts and runs empathy in the background.
Pro Free
Pro Highly maintained
You can see the activity here. For example 62 pull requests were merged from 2018-02-17 to 2018-02-24.
Pro Hosted on the web
Always up.
Cons
Con Some advanced features are lacking
Polari's users will find some advanced features lacking, such as Direct Client-to-Client (DCC).
Con May seem too simple
Unlike Hexchat or other alternatives, it does not expose much of its functionality though some of it might really be present.
Con Server, not an application
This is a server, not an application, so there's that extra bit of overhead.
Con Uses NodeJS
Javascript...
