I have it set to "Nothing" but whenever I have the window open, I can see the orange notification conter popping up on several channels (even if I mute them).

I tried leaving channels but I get invited back whenever people tag my team, so I gave up and muted all of them (but still get the notification counter, which makes muting useless for me).

EDIT: Whenever someone tags my team, the little Slack icon on the tray bar goes red... and I don't know if that's a direct message (usually important) or someone tagging my team just "fyi". I have to check it always.