Quassel vs XChat

Quassal is available for free with source code licensed under GPL and available here.

It's possible for a front-end client or multiple front-end clients to connect to a single core client. This allows setting up an always on-line core that can be accessed from anywhere.

Right now Quassel has a PPA maintainer, which allows you to install the stable version or daily versions.
Support for PostgreSQL as database backend and easy to configure for people that know a bit about systems.

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.

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.

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.

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.