My experience was that Ventrilo, Mumble, and Teamspeak had the market split between them, then Discord took it over. It's been months since I've heard of anyone using anything other than Discord, and I've never even heard of someone using Curse's client.

(Disclosure: My experience focuses on the WoW and to a lesser extent Overwatch communities, mostly in the Oceanic Aus/NZ region. But in those communities, Discord is utterly, crushingly dominant.)