When comparing KVIrc vs XChat, the Slant community recommends KVIrc for most people. In the question“What are the best IRC clients for Windows?” KVIrc is ranked 6th while XChat is ranked 8th.
Ranked in these QuestionsQuestion Ranking
Pro Plenty of customization options
Pro Still active developement
Despite whats been said, development has been continuing at a steady pace on version 4.3.1 and more recently 4.3.2.
Pro Extensive documentation available
Help files and online resources show all of the feature and scripting capabilities.
KVIrc does not need to be installed. It can be kept on a flash drive and run from there.
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 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 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 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.
Con Development stopped
The latest release of XChat was in 2010. An active fork is HexChat.