When comparing XChat vs Polari, the Slant community recommends XChat for most people. In the question“What are the best IRC clients for UNIX-like systems?” XChat is ranked 8th while Polari is ranked 12th. The most important reason people chose XChat is:
While most clients allow changing the theme or style of a window, XChat gives complete control over what it looks like. It's possible to set a custom image as the background, changing font, or syntax colors.
Specs
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Pros
Pro Highly customizable look
While most clients allow changing the theme or style of a window, XChat gives complete control over what it looks like. It's possible to set a custom image as the background, changing font, or syntax colors.
Pro Works for any level of user
XChat is an advanced IRC client that is good for beginners as well as those users who like to get under the hood. It is easy to get up and running, but has all the advanced features that a power user would need.
Pro Excellent Plugin Library
XChat has a great list of plugins and scripts. Most quality IRC clients support plugins but XChats library is incredibly extensive. There is a wide range of both useful and fun plugins. It's possible to add an RSS feed or play a game of chess. Or maybe you want to control an mp3 player via chat while translating everything you type to l33t speek. XChats Plugin Library is truly extensive.
Pro Great interface
XChat's default interface is clear, well-organized and intuitive. Channels can be laid out as both tabs and in a tree structure. All components such as user lists, topics bar or even menu bar can be hidden to provide a clean way to interact. Conversely the interface can be configured to show quick access buttons for changing channel flags, sending files or performing operator actions.
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.
Cons
Con Development stopped
The latest release of XChat was in 2010. An active fork is HexChat.
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.
