What repertoire have you worked on in the last couple years?
What technical abilities would you like to improve?
Do you like any of them more than others?
Do you have a good teacher? That will be important.The good thing about the Etudes is that each one targets a specific technique, and if you are unsure what you want to improve and have not studied any yet, I would stay start with the less technical ones. They are all demanding, but some are just downright nasty.My recommendations are:Op. 10 No. 3 (tricky middle section...)Op. 10 No. 12 (this LH will be more challenging by far than Claire de Lune)Op. 25 No 7 (beautiful LH melody)If you think you can tackle some others there are a few others that are my favs as well.
hmm.. If you can play Waldstein, you could probably play most of the Etudes.I started with Op. 10 No. 8... Then 25 No. 2. Aeolian harp 25 No. 1 is an excellent choice as well.
What grade are you? Do you even go to music school?