Your comments

I like Discord the most here since it's the only one with group voice chat. It's a shame the TOS clearly states NSFW stuff isn't allowed. I know of two alternatives you may want to consider though: Teamspeak and Mumble. They're not as easy to use as Discord, but the rules are a lot more relaxed and practically non-existent if you host your own server.

As far as text-only goes, Telegram is a fantastic service. I can't seem to find their TOS though which might be a problem.