Quick question. I understand using SimpleX and Session because those are decentralized and private options that also offer censorship resistance. However, Threema is a paid app, and as far as I know, it isn't decentralized, is it? 

Personally, I use Signal for most things, although I find myself using Matrix (through Element) for decentralized communities, as well as Session if I want to engage in anonymous discussions. I've recently been exploring SimpleX; I like the concept but I have some concerns over ownership as well as how they conduct their anonymity. Oh, and the notification spam is problematic so I couldn't see myself using it unless I'm only talking in a couple groups.