I have or have had jobs that use Slack, Teams, WebEx, Discord, RingCentral, and GChat...of all of them, Slack is superior in my opinion.
To me:
RingCental: Just...no.
WebEx: Garbage on all fronts.
Teams: Meetings sometimes bug out audio-wise for random participants and have to be restarted. I've periodically been disconnected or left a meeting and yet still get audio from it. Keyboard shortcuts are crappy. There is no Mark all as read. I can't change orgs without using a mouse.
GChat: Down there with WebEx except even shittier keyboard support and no Mark all as read. Just had a UI update and they made it worse. I hate this platform for professional use with every fiber of my being, more than Teams, about the same as WebEx. I'd rather use Lync or Skype, that's how bad it is.
Discord: Don't know why in hell any professional organization uses this, but they do. It sucks for similar reasons mentioned above in some cases. Multi-org support sucks. Alt + F4 in windows terminates it instead of doing the same thing clicking the X does and minimizing it to the tray. Notifications have issues all the time.
Slack: Multi-org support, great. Keyboard shortcuts tick ~95%, I rarely ever have to use a mouse. Huddles were pretty rough at first but at least lately I don't seem to be having any issues. Notifications periodically (maybe 2-3 incidents a year?) have issues, but are typically pretty solid.