Which Android testing framework to use?

I am learning about automatic testing for Android. There are many testing frameworks and I would like to know which one to learn. Which one is recommended/used most often.

Or if it's more of a personal preference, what are the advantages of each framework so I can choose myself.

Frameworks I have read about are: Mockito,Roboelectric(unit tests) Espresso,UI automator and Robotium (UI tests)

I would really appreciate any help as it will save my time. Thanks.