I'm using LINE and Viber. I like how easy both make it to send location links, voice or video snippets, photos, or drawings in the case of Viber.* I do have one question on them both:
Will either of them suggest contacts in my address book to other contacts? Will they try to introduce my friends to each other?
LINE does show me a list of suggested friends (tap "Friends" then the "+" icon in the upper-right corner), but I don't see this in Viber. This may be one big reason why LINE has become very popular in some places (95% of my students in one Yokohama high school use LINE; nothing else gets above 15%). Is this impossible on Viber? I don't want facebook-style introductions of girlfriends to ex-wives; bosses to sketchy, drinking friends; etc. If Viber does not do this, and commits to not adding the functionality or at least letting me control it, then I'll stay with them and recommend it to all my friends.
If you post anything on LINE's facebook style home, any one of your contacts can comment on it and any other of your contacts can see it.
I have WhatsApp installed too, but no one I know is using it.
* For those not getting the point of these chat apps over email, they make it easy to quickly utilize all their functionality. You can send the same info with email, but you have to drop out to separate apps, edit the file, then go back into the email app and send. You can do regular phone calls and video calls with some of them too; e-mail can't do that. Skype can, but it is heavy, not always running, and has its own adress book.
Edit: Viber also lets me install it on my tablet as well as my phone. LINE does not. You can carry on a conversation with whichever device you're on at the time with Viber.
Edit2: I find it a lot easier to quickly choose a sticker with viber than with LINE. If you have to search for a funny graphic, then the impact wears off, like laughing at a joke long after the conversation has moved on.