When comparing Messenger vs Ryver, the Slant community recommends Ryver for most people. In the question“What is the best team chat software?” Ryver is ranked 20th while Messenger is ranked 74th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Uses Facebook friends to create a contacts list
Allows communicating with anyone who's a friend on Facebook.
Pro Read receipts
Can see who has seen each message in group messages.
Pro Easy to share posts from Facebook
Integration with Facebook makes it easy to share any interesting posts from the Facebook timeline.
Pro Great UI
User interface of the application is clean, intuitive and easy to overview.
Pro Free
Pro Threaded conversations
Ryver has Facebook like "Posts" that allow for threaded conversations to occur among teams.
Pro Unlimited users
There is no limit to the amount of users you can invite to join your instance/account of Ryver.
Pro Upvote and Downvote
"Do you like this?" questions can easily be answered with up or down votes.
Pro Drag and drop file sharing
Start a new post, drag your file (photo, doc, pdf, etc. 100MB limit), and starting discussing.
Pro Fast
The app loads fast on start-up. Any new chats, comments, and posts show up instantly. Overall, the app just feels rather speedy.
Pro @mentions for users and teams
Get someone's attention with @mentions.
Pro Desktop and mobile apps
Apps work great on Mac, Windows, iOS, and Android.
Pro Free conference calling
Pro Can hide topics until new comment is received
You can remove a topic from your nav bar and have it reappear when new messages are sent in that topic.
Pro Hosted on Amazon
Hosted on Amazon cloud. Service is very reliable. Ryver has been unavailable maybe once or twice in the 6 month period.
Pro You can edit a chat message
With Ryver, you can edit chats that you've sent.
Cons
Con Lack of privacy
Messenger is owned by Facebook. Based on their privacy policy, this means that any information you provide (including messages sent) are used by Facebook to profile you and sell access to your data to advertisers.
Con Lack of end-to-end encryption
Secret (end-to-end encrypted) chats are only supported in one-to-one messages, and are not enabled by default, and the encryption has not been verified independently.
Con Having Chat and Posts for Teams is confusing to some users
It takes some time to get accustomed to all the features of the program, like a separate chat and a feed for team posts.
Con Don't have "emoji reaction to message" feature
