A lot of it has to do with who your enemies are.
If you're not worried about telegram, and the country telegram operates from. Then using them is probably a better idea than using a program based in a country you are worried about.
So if you're big enemy is the United States intelligence services, using a messaging service based and centralized in the United States isn't the best of ideas. Be it French government communication, or some peer-to-peer democratic revolution in a propped up tin pot dictatorship.
Simple x is interesting, but I think it's still relatively new, there's lots of UI and features that need to get hammered out. Before you would trust it operationally.
Briar is operational today, so I think it is being used by some groups. But it has limited functionality as well.
If your threat model has you communicating with people who already know who you are, registering with a phone number isnt a big deal.
A lot of the internet use of messaging, is anonymous communication, with people you don't know or trust. So giving them your phone number becomes more of an issue.
- Briar: agnostic
- Signal: "western"
- Whatsapp: "western"
- Telegram: Qatari/Eastern
- Session: "western" (centralized servers in Canada)
- Simplex: not sure where the servers are.
So if you're trying to bring women's rights to Iran, you use the Western messaging services that aren't blocked
If you're trying to bring democracy to KSA, you have a harder choice but probably telegram
If you're trying to do anything in north Korea, good luck... Dead drops and physical notes probably.
I think for the countries that block the internet completely, like North Korea and its Big brother neighbor.. mesh programs like briar might be the only viable options to organize