This is the best irc client for OSX, which is kind of sad since even this client needs lots of work. Colloquy is the best looking irc client, but lacks too many features to be usable for anyone with more needs than merely IM-like chatting. Conversation is too *unlike* a irc client to be of any interest to me.

Clients like Ircle and Snak, who was in the top in the classic days, have sunk to the very bottom with their arcane UI's. iRC is somehwere in between UI-wise, and lacks that extra Aqua feel, but still is well-thought out and handles multiple servers and multiple channels a lot better than the competition.

If you are a hard-core IRC user, this is your best bet, but don't set your hopes too high, it still needs a lot of development - especially in the scripting area.