When comparing XChat vs Communi, 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 Communi is ranked 14th. 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 Elegant and minimalist interface
Communi user interface for desktop and mobile is minimal, which helps you focus on the task at hand instead of being distracted by extra UI elements.

Pro Good ZNC integration
The author is involved in ZNC development, so the latest ZNC goodies are guaranteed to be well supported (http://communi.github.io/znc/). With help of the documented ZNC modules, Communi retains its state well across sessions. No repetitive buffer playback on reconnect, notifications and banners for newly received messages only, queries stay open until closed etc.

Pro UI runs on multiple platforms
While Communi itself is a IRC framework, the project offers several UI implementations such as desktop, SailfishOS, Meego and Symbian.

Pro Quassel protocol implementation
Communi is integrated with Quassel.

Pro Event merging
Consequent events (joins, parts, quits etc.) are merged to reduce noise and to keep focus on the discussion.
Cons
Con Development stopped
The latest release of XChat was in 2010. An active fork is HexChat.

Con No DCC
Communi does not support DCC (for a reason)

Con No scripting
Communi has no support for scripts
