Comparing Messaging Apps
Micah Lee has a nice comparison among Signal, WhatsApp, and Allo.
In this article, I’m going to compare WhatsApp, Signal, and Allo from a privacy perspective.
While all three apps use the same secure-messaging protocol, they differ on exactly what information is encrypted, what metadata is collected, and what, precisely, is stored in the cloud - and therefore available, in theory at least, to government snoops and wily hackers.
In the end, I’m going to advocate you use Signal whenever you can - which actually may not end up being as often as you would like.
EDITED TO ADD (6/25): Don’t use Telegram.