End-to-end encryption (E2E) is the only scheme one can trust to securely preserve one's communication data. As opposed to simply encrypting data at rest (on one's device and on remote servers), E2E encrypts data in transit as well, such that "middle men" cannot reasonably deduce what it is one is sending. We do not recommend any form of private communication that is not E2E encrypted. This includes email, voice chat, text chat, etc; all of these mediums of communication can be concealed and protected using E2E.
It may seem like a waste to dedicate one short article to E2E; but we cannot overstate its importance. End-to-end encryption makes one's data un-readable and scrambled to all, except oneself and one's contacts. This is why it must be used.
Several means of E2E communication are listed in DHitMA: Links to Private Communication Means.