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 8th. The most important reason people chose KVIrc is:
Help files and online resources show all of the feature and scripting capabilities.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Extensive documentation available
Help files and online resources show all of the feature and scripting capabilities.
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 Portable
KVIrc does not need to be installed. It can be kept on a flash drive and run from there.
Pro Plenty of customization options
Pro Terminal-based
Screen multiplexing and remote connection options with screen or tmux.
Pro Themes
Allows the modification of IRSSI's look and feel.
Pro Free and open-source
Pro Quick and easy setup
3 or 4 commands and you're ready to chat with all your old friends.
Pro Perl scripting
Allows the user to create and use perl scripts to perform actions.
Pro Command line outputs can be sent to a channel or message
/exec -o figlet "Slant.co"
Pro Easy logging
Pro Persistent connection
Pro Has a plugin for encrypted communications
Cons
Con No GUI
Actually a plus for some, lower memory overhead.
Con Gives little direction upfront
Actually, Irssi.org has it's own GREAT documentation for new irssi users. Inline /help options are pretty well documented.