Mumble/Murmur and Teamspeak have better voice functionality than Discord, because they really are designed for voice chatting.

> But not in text (Mumble severely lacking, Teamspeak marginally better).

Concur, and this, along with all-in-one Slack-like rich URL handling leads to selections of discord.

A more OSS friendly stack of Pidgin + Daemon | IRC & Mumble/Murmur seems to have the best scaling, and the best of both worlds, at least in my opinion because it has the lowest cost, richest functionality, and can scale the highest in terms of users without being dependent on a commercial service. I say this because I have seen Mumble/Murmur with > 2000 active users which is possible due to the rich permissioning system and excellent performance.