[throwaway89201]

Meta sees your entire social graph by design, and stores the name and participants of groups you create. You (meaning: experts) can independently audit and through reproducible builds verify that Signal does not do this by design, while nothing about WhatsApp can be audited in the same way. Meta is also a plainly for-profit company with bad track record, while Signal often gets flak from (IMO mistaken) radical nerds but otherwise has a very good reputation.

The privacy fatalism in your comment here and in other comments is plainly incorrect.

[ezst]

What you say is barely different from what the opponents to generalized https were saying back in the days "true your ISP can see all your traffic, but they are the good guys, you are their customer after all".

With SSL, we no longer have to care, and that's much better that way. Signal has all the same means of (meta)data harvesting and analyzing as Meta. It can't be made different: this is built into their very centralised service. All I'm saying is that we should aim for better, and have guarantees baked into the protocol to avoid absolute metadata centralisation. Federation is a good start.