Few notes on this (and going to fork discussion by quoting you to maintain all due credits, if you don't mind).
1. Neither of these 4 are decentralized. By "decentralized" I specifically mean that the system does operate without ANY central infrastructure in peer2peer+DHT style, central server used for hash table bootstrap may be an acceptable compromise. Briar may be a good example of decentralized platform.
2. You're missing the context both in terms of threat model and use case, which makes the choice between the 4 pretty vague, like "just some 4 privacy messengers".
3. First question one should ask when choosing privacy tools: "Who's the adversary?" 2nd key question is individual definition of privacy.
4. Govt imposed blockings and restrictions are rapidly becoming problem #1 in private communications land and must be considered as a factor of platform choice.
5. Endpoint device is the most successful attack vector, in practice. Thus, features improving endpoint device security (e.g. "panic button") should be considered as well.
