Pinterest when was launched got a lot of popularity but with the time website got tough competition from Instagram both the website got same type of concept of photo sharing.
But Instagram is more good than Pinterest on app in android as well as iPhone .
Same time the Pinterest is much better than Instagram on website.
Both are good at there place like for PC User Pinterest has great interface and ui
At same time for Android User Instagram app is Better than Pinterest app.
For online I will definitely recommend pinterest, But not for smartphone user.