There are plenty of apps in the android play store which provides the feature of video calling like IMO video calling, Google Hangouts, Skype, etc., But Google Duo has its own image it got 1 million downloads in first week of its release.
Google Duo provides the feature of video calling and it is most simple and useful interface in my opinion the app is very light and uses very less space on ram and phone memory and give you the power to video call .
The registration is also very simple and its quite popular.
If you are looking for a video calling app on android play store then Google Duo is Best in My opinion.