I prefer the fluent style because you must not think so much. Just use the smart code completion by pressing "." and select what to check.
The assertJ-android provides extra some checks for android elements like assertThat( textField ).hasText( "expected text" )
Add to your test dependencies 'com.squareup.assertj:assertj-android:1.1.0'
and use assertThat( actual ).isEqualTo( expected )
instead of assertThat( actual, is( expected ))
Import both assertThat methods to use automatic the correct one.
import static org.assertj.android.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThat;