My company just switched to Teams (from Sametime). We had evaluated Slack, Teams, and Cisco/Webex Teams. To me Teams is a pretty crap chat tool, but it's integration with WIndows (and the macOS client isn't shabby either) is what made it a clear winner. We can chat, do voice, share files, collaboratively edit files, share desktops, all in one app. My only complaint is that the emoticons are typical Microsoft style and should be updated to something better. But this might be due to most Windows desktops not using a high DPI. On a Retina screen they look amateurish.