When comparing GroupMe vs Yammer, the Slant community recommends Yammer for most people. In the question“What is the best team chat software?” Yammer is ranked 37th while GroupMe is ranked 49th. The most important reason people chose Yammer is:
To make it easier to learn for new users and increase adoption.
Specs
Ranked in these QuestionsQuestion Ranking
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 User interface is modelled after Facebook
To make it easier to learn for new users and increase adoption.
Pro Hashtag support
Hashtags help organize projects and parts of projects easily. Great for getting an overview of a specific subject and seeing if something's missed.
Pro A complete social network for business
Yammer works like a typical social network with status updates, comments, file sharing, groups, etc.
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 Lacks customization options
