I’m talking about GNU here.
I just can’t seem to figure out on how to use either of them to communicate. IRCs don’t save older messages, but instead logs them. And I guess for the same reason, it is impossible to discuss anything in depth.
Mailing list is really hard to read, as it is nowhere similar to forum or tree-style comments. I can’t figure out what mailing list to message to.
IRC I think is more intended for live discussion in the moment. It connects you to chat rooms, and is not suitable as a persistent messaging app.