We use both slack and Teams extensively. Slack is more our corporate “social” area, where quick questions or channels on topics exist.
Teams is used more for business and project-centric stuff, where you have files and project data and other stuff you collaborate on with a “team”.
We used to use Skype before migrating to Teams, and we use zoom extensively for video-con (teams is still a little weak there). At first I didn’t like Teams but after having a 1 hour training with my direct reports, I think it has a lot of promise, especially in our new remote world. It’s a great tool when you have globally distributed teams.
SF acquiring slack will probably ruin it.