The tinfoil hat part of me has been seeing this push for the Signal protocol straight out of nowhere and am a little worried its being done by a state level actor who knows something about it that we don't. Its much younger than PGP and as such has had less eyes on it. I also don't think Moxie Marlinspike, the founder of Signal's owner - Open Whisper, has the cred and trust Phil Zimmerman had, at least not yet. Its particularly worrisome as he seemingly is only known by a pseudonym.
I also would consier S/MIME, which is baked into most feature-heavy email clients including iOS, a practical alternative to PGP when the use case is email encryption. You and a friend can get certs easily, put them in your client via GUI, and be done with it. No command line skills needed if ease of use is the big complaint here. For the less technically inclined its a pretty good solution, pun intended.