I have been using WhatsApp from last 2 years as my primary messaging app. It’s concept is very good that only person with your phone no. can contact you. It is so user friendly that even my father uses this messaging app. There are many features in it which I love very much such as calling feature and now they have launched video calling which offers very good calling even if you have slow internet. It also shows that whether your message have been received by other person or not and they have seen it or not.
There are few features that must be added such as we can permanently leave a group and delete messages from other’s person chat history also.