When comparing GroupMe vs Allo, the Slant community recommends GroupMe for most people. In the question“What are the best messaging apps for iOS?” GroupMe is ranked 21st while Allo is ranked 30th. The most important reason people chose GroupMe is:
GroupMe has a built in function to read receipts.
Specs
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Pros

Pro Reads receipts
GroupMe has a built in function to read receipts.

Pro Great web client
GroupMe has an excellent web client that can be used to send and receive messages and manage groups from the desktop.

Pro IFTTT Integration
Allows sending messages from web services via IFTTT.

Pro Integrated calendar
It's possible to add location and time with reminders directly in the GroupMe app.

Pro Makes it easy to silence 1 or all groups
GroupMe has settings that allow muting a single group or turn off all GroupMe notifications from within the app.

Pro Does not require everyone in the group to have a smartphone
GroupMe can set up a custom phone number which allows people without the App to send and receive messages. This makes it easy to add anyone to messaging.
Pro Persists history
Your chat history is persisted by default (you can send incognito end-to-end encrypted self-destructing messages instead if you so desire).
Pro Allows self-destructing messages
You can send messages that will be removed from both parties after a defined period of time.
Pro Allows end-to-end encrypted incognito messages
Pro Assistant
The assistant is a bot that can help book, look up locations, restaurants, set up calendar events, etc.
Pro Full quality pictures
Cons
Con Drains battery fast
GroupMe, in order to have a constant connection which allows for notifications drains the battery of a device quickly, which is not ideal for a messaging app that one needs on time notifications from.
Con Not yet released (should release in summer 2016)
