Based on the level suggested by your pieces recently studied, along with your preference for Mozart or Beethoven, I would suggest Beethoven #1 or #3 (although, as suggested by AC, the #4 has a beautiful level of romanticism which separates it a little from earlier, and more classical, works - but is a little more difficult than the forementioned works). The Mozart D Minor K 466 concerto is also a rewarding classical work to play.
All the best in learning your chosen work.
Ian