When comparing WeChat vs iMessage, the Slant community recommends iMessage for most people. In the question“What are the best Skype alternatives?” iMessage is ranked 17th while WeChat is ranked 35th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Friends can be added by scanning a QR code
WeChat generates a QR code for each user that other can be scanned to add them as a friend.
Pro Can be used as a Walkie Talkie
WeChat has push-to-talk functionality that can be used both one-on-one and in groups.
Pro Large collection of animated stickers
Pro Easy to send voice messages
Users can record a voice message from within the app to then send it to a recipient, who can then play the message from within the app. It is all self contained.
Pro Enables meeting new people
WeChat has a feature that pairs random people for a conversation. It is activated by shaking the phone (requires location sharing to be enabled) and will present a list of people who are doing the same and how far away from you they are.
Another feature for meeting new people is the Friend Radar that will display people in your vicinity that can then be added to your contacts list.
Finally, there is the People Nearby feature which allows you to send and receive greetings from people in your vicinity.
Pro Moments social network is seamlessly incorporated
Pro Flexible creation of chat groups
You can create chat groups for up to 500 people.
Pro Filters for photos
WeChat includes a collections of filters that can be applied to photos to change how they look.
Pro Secure end-to-end encryption
Pro Cross-platform within Apple ecosystem
iMessage is available on iPhone, iPod, iPad, and Mac.
Pro Supports voice messages
Short voice recordings/messages can be quickly sent, and messages can be easily dictated into written messages as well.
Pro Free and unlimited messages over Wi-Fi and data
Messages clearly indicates whether messages are being sent over iMessage (blue) or SMS (green) where messaging rates apply. iMessages do not count as SMS messages with your carrier, instead they use a negligible amount of data to send over Wi-Fi and cellular data networks.
Pro Clear indicators for message delivery and receipt
The app indicates when messages have been sent, when they have been read, and when someone is typing.
Pro Comes pre-installed
No need to download or sign up for a new service.
Pro Seamlesss switching between SMS messages
Pro Friends don't need to "sign up"
You can just message them using their existing phone number or Apple ID and they will get your message.

Pro Clean UI
UI is minimalistic, and clear. And there is a plethora of stuff on the left of text box if you wanna use them.
Pro Apps and games for iMessage are available
For example, you can play games like pool or you can show someone a destination to go to.
Cons
Con Notifications get muted after inactivity
New message notifications stop getting pushed if the application isn't opened for some extended period of time (seems to be around a week or so)
Con WeChat complies with China's requirements to hand over data
Con Conversations and chat groups aren't ported to new devices
Messages are stored on each device, so shifting to a new device means losing all the previous conversations, as well as an inability to post in previous chat groups until someone else posts there and you're alerted of a new message.
Con User base outside of China is comparatively small
While WeChat has over 400 million users the majority of them are in China. Adoption in other markets has been slow.

Con Not cross-platform
iMessage is not available on anything but Apple devices.
Con Can't send separate texts to individuals who share a Contact record
iMessage is an utter disaster. It can't send separate texts to anyone who is on a shared Contact record but with separate mobile phone numbers (e.g., "Paul and Angie Smith"). It merges ALL threads that ever went to ANYONE on that shared Contact record. Want to text just the husband to set up a surprise party for the wife? Not possible. iMessage will ONLY add that new text to the EXISTING thread you had with the wife. Duh! iMessage is pitifully incompetent.
Con Blocking Spam Messages takes 3 steps more than is needed
You have to open the message, select the sender, open info on the sender, then block sender. The default Android message app, select the message, block sender. it automatically deletes the message and blocks the sender.
Con iCloud sync of message is not stable
Sometimes, the messages on different devices with the same ID will be different, the syncing function work poorly.
Con Slow and unreliable
