FUN FACT: WhatsApp is encrypted and HIPAA-compliant. The other two are not.
I don't see this ending well.
With a reasonable degree of confidence, Signal is the best secure messaging app. It's open source, audited, and e2e encrypted. Whatsapp started using Signal's encryption as well, but Signal doesn't share data with Facebook. Also, a reminder that currently, Facebook can and does read Messenger's messages. It reads the text and also follows any links in the messages, and uses this info for advertising purposes. My main concern with this move is that Facebook will start keeping and using the metadata (who you send messages to, and when), correlating it with other data (where you were when you sent those messages, whether or not you're FB friends with this person, what groups you're members of, your political leanings, etc), and using it for its own purposes. I am also concerned about Facebook outright breaking or backdooring the end to end encryption on Whatsapp and using the new backdoored encryption for all three services.
I've been using Signal for a while now but it doesn't have push-to-talk the way WhatsApp does, which allows my wife's practice (and, as a consequence, about three other practices - it's spreading like a virus) to use WhatsApp like a HIPAA-compliant Nextel walkie system. I am concerned about Facebook ruining it a million different ways, including those you list. Considering the fact that WhatsApp has been used for (A) distribution of child porn (B) fomenting of lynch mobs, they have the political cover to gut it however they want.
Unless I'm misunderstanding what you mean, Signal now has push-to-talk voice messages. I haven't used the feature in either service, so maybe they differ in some usability way. And I agree, censorship is popular when it's framed as preventing concrete harm in the present at the risk of potential greater harm later on. Most people will accept that bargain.