Between the two, I think mostly that slack is better, but it could be that I've spent the time using it, and the keyboard shortcuts have become life (not sure, does teams have keyboard shortcuts?).

Where teams wins is subthreads. Slack only allows on thread deep, which is awful when everyone here insists on threads. And then those threads become a random mind map and often don't actually map back to what started them.

I much prefer IRC and no threads (and none of this emoji shit), but I'm also #old.