I have used Jitsi. Last week I did a few pairing sessions where the both of us were sharing our screens and still had our webcams on in the corner and it was awesome.

We tried to do a standup with (I think) 8 people and it was terrible - people would randomly not get any audio for stretches of time, video would get choppy or lost completely, it was not pleasant.

I will keep using it for pairing since I haven't found another tool that gives me that kind of flexibility and it was in fact very good. I believe the whole experience is limited by the connection quality of the worst participant.

I haven't used Jitsi, but different apps and approaches work better in different situations. Are you screen sharing? Audio chat? video chat? Large meeting with multiple people? Mac/Win/Linux? Is your connection bad? High latency? Low throughput? No solution was very robust and if you're working internationally and people have their own equipment it can be a mess. People are also get really familiar with one piece of software and hate installing yet another.

The churn between companies like Google and Microsoft (each offering, and deprecating multiple solutions) doesn't help.

Jitsi Desktop uses SIP (never used it)

Jitsi Meet (browser client) uses WebRTC, and is really nice!