When comparing KVIrc vs IRSSI, the Slant community recommends KVIrc for most people. In the question“What are the best IRC clients for Windows?” KVIrc is ranked 6th while IRSSI is ranked 9th.
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 Perl Scripting
Allows the user to create and use perl scripts to perform actions.
Pro Persistent Connection
Pro Command line outputs can be sent to a channel or message
/exec -o figlet "Slant.co"
Allows the modification of IRSSI's look and feel.
Pro Free and open-source
Pro Has a plugin for encrypted communications
Con Gives little direction upfront
Actually, Irssi.org has it's own GREAT documentation.
Con Cryptic configuration files
Con Can't do vertical splits
Untrue, there are perl scripts available to do split screens with
Con No GUI
Actually a plus, lower memory overhead