Streaks has been my habit tracking app of choice on iOS for several months now. It's so easy to use and the integration with the Health application on iOS is great.
Now, they have released an update which provides:
a widget, allowing for quick entry of habits from the Notification Centre
the ability to use 3D Touch on the Home Screen to mark a habit as complete.
It's a great update to a great application. Grab Streaks here!