I can vouch for Zoom, I use it daily in chats with 5-10 people in 5+ countries and frequently with more, it works flawlessly given a decent connection (basic DSL).

I wish the UI was a bit better though (e.g. consistently working way to see who is talking is a feature that is not there or, it seems, sometimes it is and then disappear).

Zoom is pretty awful, we have constant issues with audio quality.