What's best to choose - NoSQL or SQL - for a large chat application?

So here is the situation, I'm working on a chat application (internal chat application) with abilities to handle too many messages and maybe scale it further. What I'm working on is User with multiple private channels (chat rooms one to one), and create groups as well. but database selection part is taking away a lot of time which I should invest in developing the app instead of wasting it. Thats why i'm here to ask professionals what you guys really think about selection of right database for this particular type of web app / app

tech stack: Angular (front) ... Node.js (backend), Socket.io , DATABASE(pending)

So my questions is Which one you would choose and why you would choose it? Only if possible for you to take out a little time. Can you provide a little example of written schema of Relation as such:

User Channels (chat rooms) , connected to above user Document / Table Messages (messages connected to chat room along with sender reference), connected to user and channel document / table

For Mysql I'm clear, I've used MongoDB but I'm a little confused regarding it. Would be awesome to have my mind cleared with your learnings and help me out to choose the best.

Let me know if you need further clarifications :)