In the past, I went from Ventrillo to Teamspeak 2 and now to Discord. I've never even heard of mumble.
I remember when we used skype for voice chat... back in the days... Haven't used voice chat things in 4 years, so I can't choose between discord and mumble.
Believe it or not, I still use mind from time to time. I used to be the dude in mc chats, "What is your Skype name, lets chat" Good old days of mc right there.