We started in phase and then gave OOP a try. We liked it and stayed that way for several years (gave stoker a sense of her own power contribution), until we got our new bike and gave in phase a try again. Been in phase for past year and half with no interest in another OOP trial. Bike seems a little easier to control in phase, although a techinically correct "spinning circles" pedal technique seems to minimize this - power application is ideally fairly constant all around each pedal stroke.