Well, it actually depends what's your ability and what are your strength and weaknesses.The Ballade is certtainly Grieg's most ambitious and difficult work for solo piano, but it doesn't compare to Liszt or Chopin etudes, at least in my opinion.I would rank it among Chopin polonaises for technical skill (it's a variation work , so some sections have lots of octaves or skips and others are relatively easy to pull off).It's weird that you want to learn it, cause most people haven't even heard it (Rubinstein made a good recording, though). I find it difficult to make it sound logical in structure.