When comparing Signal vs Disa, the Slant community recommends Signal for most people. In the question“What are the best messaging apps for Android?” Signal is ranked 1st while Disa is ranked 14th. 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 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.

Pro Does what it's supposed to do, without bloatware

Pro Open source plugin API
Everyone can develop their own plug-ins.

Pro Easy to use
Disa is very easy to use and has an open source API, so many new services will be added soon.

Pro Customizable notifications
Ability to set different notification sound/vibration/led based on the plugin.

Pro Unified conversations
Ability to merge conversations from the same contact on different services.

Pro Friendly developers and generally good G+ community
Fast, decent replies to questions, even if they've been asked before.

Pro Many requested features
The developer team does actually listen to the community and adds requested features.


Pro Pushbullet support
Disa works great with Pushbullet, allowing you to answer from your PC.

Pro Many languages
Help and support in many languages.

Pro Disa takes privacy much more serious
Currently, the Disa team knows less about you than the website you're currently visiting.

Pro Great material design
With color-changing design with custom colors for each service.
Cons
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.
Con Doesn't support most messaging apps

Con Disa doesn't follow the Google Design Guidelines
Hamburger Menu/Navigation Drawer (Side Menu):
https://www.google.com/design/spec/patterns/navigation-drawer.html#navigation-drawer-contentNo Animations:
Empty Pages/States:
Maybe a Launch screen?:
Con Does not support Google SMS
Con Closed source
Disa is closed source, so the development speed is capped of their team, no external developer can help or add features that are not on the route of the team.
Con Doesn't support WhatsApp at the moment
Con Attaching pictures suddenly failed; no working solution.
Con Smaller development team leading somewhat slow implementation of requested features
Though the main development (framework, etc) is moving along fine, things like quick reply and sending multiple images at once should've been in quicker.
Con Constantly asks to re-authenticate WhatsApp
Con Doesn't let you customize notifications per conversation or contact
