When comparing Messenger vs Handcent Next SMS, the Slant community recommends Messenger for most people. In the question“What are the best messaging apps for Android?” Messenger is ranked 21st while Handcent Next SMS is ranked 36th. The most important reason people chose Messenger is:
Allows communicating with anyone who's a friend on Facebook.
Specs
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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 Can split a group text
Splitting a group text is a great option, so that follow-up can be personal and not everyone sees every response.
Pro Missed notification reminders
Pro Can text from a PC, Mac or tablet
Texting from another device allows one to not pick up one's phone every minute.
Pro Customizable appearance
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 Name is confusing
In your app drawer you'll see "Next SMS" but in Google Play "Handcent" is the first word of the app. That might confuse some people.
Con Texting from a PC, Mac or tablet requires extra work
