For console, irssi by far. (weechat manages to use more memory than some gui clients on my system, and it just feels bloaty to use, even sluggish at times - ymmv depending on plugins used and support for what scripting languages you compile in). Honorable mention to the OG BitchX client and of course ircii ;)
If you are in a LOT of channels on many different networks, irssi can be a bit of a pain to manage, but it’s made better by running it with AWL (Advanced Window List) inside a tmux session (tmux is optional, but if you don’t use tmux, it will spawn an extra X window instead, it seems it’s not compatible with GNU screen alas).
Beyond that, Quassel is quite nice; it has a server and client component. This means you can throw the server up on any 'old machine (an actual server or an rpi in the attic somewhere), and as you connect with your client(s) you will retain chat history, and stay connected to IRC. There’s actually multiple clients for quassel - you have the official GUI client for desktop, which is quite nice, and does a really good job visualizing which channels are on which network if you configure it to do so. There also is an official android client (which imho is THE best mobile irc client i’ve ever seen so far - unfortunately all the IOS clients I’ve seen are garbage). Multiple clients can be connected to the same quassel server at the same time, so that means you can switch between desktop/mobile and just resume a conversation seamlessly. That’s kind of a big deal, if you can’t be bothered to set up a bouncer like ZNC. (I actually use it in combination with znc, heh) - there also is an irssi module to allow irssi to talk to a quassel server as well, if you still want to use irssi - My only complaint with their GUI client is that it doesn’t seem to support DCC transfers, which is really unfortunate (it also doesn’t seem to support CTCP)
Other than that, I’ve also always been quite fond of kvirc - it has a lot of features, and is very customizable for a gui client - and even has scripting support - closest thing resembling MIRC that you will find on non-windows platforms imho.
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