Oud in general is more difficult in the beginning than these two instruments and this is due to the fact that it’s a completely melodic and has no predefined sets or keys like the piano keys or the frets on the guitar. However, that does NOT make the Oud the more difficult instrument to play in the long term. Developing techniques and skills on the Oud should get easier as the time go by, as long as the student follows an academic method and doesn't develop bad habits that don't get corrected by a teacher.