If you really want a chat tool to start a revolution, meet in person with people you trust and don't bring any electronic devices with you. And only talk to people who you really trust. Forget phones.
At rallies, masked, sun glasses, baseball hat and a couple of shirts
Anyhow, a combination of the two is likely best. It won't really help though, "back in the day" every movement had a few police informants in the mix. There's less of that now with electronic monitoring, and 24x7 tracking, but a totalitarian state likely has more of that mix.
Heck a bunch of crooks tried to rob my house, and were caught not only due to having their phones on them, but ALSO due to sending SMS messages about houses they were examining "This house looks empty!", but also because they dropped a phone outside my house, when fleeing when the alarm went off... and the phone wasn't even locked!
Just imagine in a police state. I think a lot of revolutions get stopped before conspirators even get to the "protect our comms" point.
a super power I wish I had.
https://en.wikipedia.org/wiki/Qatari_involvement_in_higher_e...
Stochastic terror and the stochastic coup work great precisely because there are no clear unambiguous two-way communication trails between the instigator and the accomplices; just a lot of "wouldn't it be great if somebody did something". Fell apart afterwards because there was no further planning.