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I use Textual, well worth the $5 it costs.

Try LimeChat. The interface is good and I have used it every day with no problem.

irssi, textual, or IRCCloud (if you care about a mobile client as well) would be good. Textual over Limechat because it is a forked version of Limechat and is much improved in terms of functionality.

try https://www.svyft.com .

macirssi is popular if you want a client with a GUI.

I just use Adium.

limechat (osx) is decent.