When comparing IRSSI vs Adium, the Slant community recommends IRSSI for most people. In the question“What are the best IRC clients for Mac?” IRSSI is ranked 6th while Adium is ranked 7th.
Ranked in these QuestionsQuestion Ranking
Pro Persistent Connection
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"
Allows the modification of IRSSI's look and feel.
Pro Free and open-source
Pro Has a plugin for encrypted communications
Pro Easy-to-use interface
Pro Open source
Pro Supports file transfers
Pro OTR encryption
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
Con Appears to be abandoned
Not Gatekeeper-compatible, SSL cert expired, social media presence is ancient.
Con Lack of multi-resource message capability
No carbon copy, for example.
Con Lack of OMEMO encryption
the de facto standard for Jabber Texting [xmpp]
Con No antispam (built-in or by plugin)
It has no challenge-like antispam (such as seen on github.com/jesobreira/box-sentry plugin for pidgin).