Hi Janet (and everyone),
That's a great question. I think of this Google Group as the official channel for announcements. It has the most subscribers at 1051, as of this writing. It's also a fine place to bring up an idea for discussion.
Zulip is more modern, and while at first blush it looks a bit like a forum, it feels like chat when you're in it. You can see when people are typing. You can reply back and forth quickly. You can send direct messages. We're using Zulip for working groups (#docs, #python, #containers, etc.) and #troubleshooting is a popular channel, where clarifying questions can be asked and answered.
Thanks,
Phil