I would recommend you start with whatever looks best to you, then keep trying solutions with friends who are up for it until you've found something that works.

I would recommend you start with whatever looks best to you, then keep trying solutions with friends who are up for it until you've found something that works. This question is also really dependent on your own and your friends' threat models so general advice is only marginally useful here. Personally I use Telegram because there's a distribution of it on F-Droid. If you do you should consider telling your friends to only use secret chats since only those are encrypted end-to-end. Signal has some nice features like not storing your in-app contacts on their servers and the "sealed sender" feature which largely hides who is talking to whom in a conversation. As for the others I can't really comment on them. Maybe another option to consider is Briar[1] which works entirely peer-to-peer over Tor, Bluetooth or the LAN and defers sending until both devices are online at the same time (which might work for phones). [1] https://briarproject.org/ https://briarproject.org/