Textual is good. It costs money but it's GPL'd so you can build it yourself for free in a matter of minutes, there are plenty of tutorials online.

+1 for Textual, and for building it from source.

I am behind a firewall at work so I use web clients. I used to use https://kiwiirc.com/nextclient/ but now I've moved to https://www.irccloud.com/ (the free version).

I use Colloquy on the mac.

Colloquy. Desktop version more or less hasn't been touched in 8 years, and it remains the best Mac client. Also has an iOS version that is more recently maintained.

I use weechat on a mac. Works just fine with iterm2. I press cmd-~ and it pops up on screen.