I used Whatsapp and personally like it better, but I like Kik's ability to tell you when it is sent\delivered\read while Whatsapp just tells you if its sent\delivered. I don't need group chat so that's a moot point for myself
Couple of gripes I have with KiK and had to get rid of it. From my limited use (2-3 days), I learned:
-you cannot log out of KiK.
-it automatically adds contacts without your approval and worse, it lets these contacts know you've signed on to KiK as well. I dont know about others but I dont necessarily want IM access to everyone in my contact list.
-it adds people that you dont even know (saw ppl on my list that I dont know) to your contact list.
-You can get random requests from ppl you dont know to add you just the same.
It seems like a very good beginning efforts but more control and privacy measures need to be put into before I'll try it again.
And, lastly, it was draining my battery ...
These are all from personal use and observation.