Catalin Cimpanu for The Record: FBI document shows what data can be obtained from encrypted messaging apps. These are the things that a skilled intellegence agency can get legally from different messaging apps. This is important, because this is also the things that someone else could get illegally. Signal appears to come out on top on this list (I do donate regularly to the Signal Foundation).
Depending on how thick your tinfoil hat is, there actually may be even better messaging apps though. Take a look at PrivacyTools.io’s messaging apps list.