I try to push Mumble over Skype, the main issue with Mumble is that it's not as easy to get into. You spend too much time configuring your client, finding a server, etc. Things that should be fairly trivial. Then you may spend more time figuring out why you're not being heard, or why nobody's hearing you. Mumble is great but there's too much friction involved. I prefer Discord[0] because it's so easy to use by comparison, to test it you don't even need an account, you just run it from your browser. I just wish Discord had a Linux Client.