When comparing KVIrc vs Quassel, the Slant community recommends Quassel for most people. In the question“What are the best IRC clients for Windows?” Quassel is ranked 4th while KVIrc is ranked 8th. The most important reason people chose Quassel is:
Quassal is available for free with source code licensed under GPL and available [here](http://bugs.quassel-irc.org/projects/quassel-irc/repository).
Ranked in these QuestionsQuestion Ranking
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 Plenty of customization options
KVIrc does not need to be installed. It can be kept on a flash drive and run from there.
Pro Extensive documentation available
Help files and online resources show all of the feature and scripting capabilities.
Pro Free and open source
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.
Pro Easy installation on Ubuntu due to the existence of PPA's
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.
Con Potential memory bloat in monolithic client if left running for a period of time
(I don't know if this problem has been fixed in recent years, but I have doubts)
Con No DCC support
DCC or Direct Client-to-Client protocol allows for private communications between users (without the traffic being routed through servers). Neither chat nor file transfers are supported.