When comparing Google Allo vs Signal, the Slant community recommends Signal for most people. In the question“What are the best messaging apps for Android?” Signal is ranked 1st while Google Allo is ranked 22nd. The most important reason people chose Signal is:
Signal uses an advanced end to end encryption protocol that provides privacy for every message every time.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Integrated with Google Assistant
Automatically shows options for restaurants/movies/etc when relevant according to the context of the conversation. It's also able to perform actions accordingly like order tickets.
Pro Supports end to end encryption
You can send end to end encrypted message that will auto-delete themselves after a specified time.
Pro whisper SHOUT let's you express yourself through text size
You can easily adjust the text size to show either a whisper or a shout, adding emphasis to your messages. Simply hold the send button and slide up (to shout) or down (to whisper).
Pro Message can self-destruct after a certain time
You can send end to end encrypted message that will auto-delete themselves after a specified time.
Pro Animated stickers and emoji
Some shouted emoji animate and you can download additional stickers and send animated stickers.
Pro Full resolution picture sharing
Pro Smart replies
Part of the Google Assistant is providing common answers based on your conversation thread (like in Gmail/Inbox).
Pro Themes
Each chat's theme can be changed to one of a few themes. Some themes even have specific chat colours for each user, making it easy to see who is talking.
Pro Can share a location
Share your current location or any place with other people.
Pro Encryption on-the-wire and in cloud storage
All messages are encrypted while in transit and on Google's servers.
Pro File sharing
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 Supports encrypted group chats
Pro Has a desktop app
Signal Desktop can be used on multiple devices and has most features of the Android version, although it still requires you to register with your phone.
Pro Supports sharing of various different media types
Signal supports: emoji, pictures, videos, audio, contacts, any location and GIF.
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 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 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 Works everywhere in every country
Unlike most messenger apps, Signal works reliably in all countries by securely circumventing internet censorship.
Pro Recommended by Edward Snowden
Edward Snowden uses this messenger and recommends it to everyone who is concerned about his privacy.
Cons
Con No web interface (yet)
Currently there is no web interface to send message using your computer. Project leads have teased screen shots of the web interface.
Con Few users currently
Allo was just released in September, 2016 and it doesn't have a very large following yet. We haven't yet seen how popular it's going to be.
Con Exclusive
If your contacts aren't on Allo it is worthless, and no one is on Allo. Tried it after Hangouts fail, discarded it within days.
Con History deletes on sign in
If you uninstall the app or migrate to a new phone your messages history is deleted. This, despite the fact that Google keeps a copy of your messages permanently for data crunching.
Con Single device
Part of reliably saying if one saw your message, and having it tied to a phone number, is that you cannot have the same Allo account on two phones.
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 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 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.