I'm not sure if it's a better choice for everyone. With mumble you'd need to maintain a server, for instance.
If your primary concern is open source then mumble/jabber is probably your solution
If your primary concern is open source then mumble/jabber is probably your solution
If you're truly paranoid there's a Mumble port for OpenBSD, though that obviously wouldn't fit Stallman's definition of Free.
Until we moved to Discord. Which has equally good sound quality, a fantastic chat and role system, and the ability for people to just jump into your voice call instead of having to be invited (which was what killed Skype for us, for any number of people over 3).
I'm part of a bunch of guilds for just hanging out and playing video games. But I also moderate two Discord guilds for programming, containing thousands of people.
Discord's pretty sweet, in a way that Skype and Mumble simply can't compare.