When comparing Signal vs Email + PGP, the Slant community recommends Email + PGP for most people. In the question“What are the best ways to transmit sensitive information over the Internet?” Email + PGP is ranked 2nd while Signal is ranked 3rd. The most important reason people chose Email + PGP is:
The original version of PGP is no longer freeware since it was aquired by Symantec, but the source code can still be [downloaded](http://www.symantec.com/connect/downloads/symantec-pgp-desktop-peer-review-source-code) for peer review.
Ranked in these QuestionsQuestion Ranking
Pro Provides security and privacy
Signal uses an advanced end to end encryption protocol that provides privacy for every message every time.
Pro Free and open source
Signal is free and open source software, enabling anyone to verify its security by auditing the code. It's the only private messenger that uses open source, peer-reviewed cryptographic protocols to keep your messages safe.
Pro SMS/MMS support
Signal can be your default SMS/MMS text messenger. Encryption is not possible when sending SMS to your contacts, however.
Pro Supports encrypted group chats
Pro Supports sharing of various different media types
Signal supports: emoji, pictures, videos, audio, contacts, any location and GIF.
Pro Recommended by Edward Snowden
Edward Snowden uses this messenger and recommends it to everyone who is concerned about his privacy.
Pro Message mirroring on Signal Desktop
Signal Desktop is a Chrome extension that allows you to mirror messages from your phone, including replying.
Pro You can easily view all media exchanged
You can easily view all media shared in the chat without scrolling back to when it was shared.
Pro Note to Self feature
Allows you to "send: messages to yourself and sync to desktop so you can use Signal as a kind of encrypted Pushbullet alternative
Pro Works everywhere in every country
Unlike most messenger apps, Signal works reliably in all countries by securely circumventing internet censorship.
Pro Annonymous Sender (Encrypted)
The sender credentials can be encrypted with the rest of the message, leaving only the recipient address readable by the Signal server. Even if Signal wanted they couldn't see who is talking with who by this mean.
Pro Code available for audit
The original version of PGP is no longer freeware since it was aquired by Symantec, but the source code can still be downloaded for peer review.
Pro Many implementations available
PGP is a protocol and not an application per se. It offers a standard on which applications can implement to offer full encryption.
Pro No need to exchange private keys
PGP uses asymmetric encryption. One user generates 2 keys - private and public. Another user uses the public key to encrypt the message that can then be decrypted only using first users's private key.
Pro Can be integrated with multiple email clients
Con Needs access to your phone number and contacts to work
Con Single device
Signal can only be registered to one mobile device at a time. But you can link Signal to Signal Desktop.
Con Unreliable notifications
Sometimes messages won't be received if the Signal app has been closed for a long time or hasn't been opened after booting the device.
Con Servers hosted in the US
A security risk due to National Security letters, which require giving up data to the US state, and making it illegal to disclose that.
Con If SMS/MMS imported, other apps can't read SMS
For those using Join, Pushbullet, or similar apps to send and receive SMS/MMS from web or desktop, putting your SMS in Signal somehow breaks this functionally. The dev is aware but plans to remedy the situation have not been named a priority.
Con Cannot work w\o Google services
Signal relies on Google services for push notifications so although it is encrypted and open source it needs proprietary component to work. That means you can't use Signal on some custom Android ROM (preferably rooted for full control) without Google apps installed.
Con Uses message mirroring
Con Your contacts also need PGP
It's difficult to make all your contacts use PGP. Not everyone is 'privacy focused' and willing to learn/implement PGP.
Con Can be daunting to set up
If your email client doesn't support PGP encryption, decrypting e-mails ca be dauting, especially if you want to stay away from command line.