Why not play the second ballade or the second scherzo? Those are easier than the sonatas and the first ballade but still really challenging and you can learn a lot in those pieces.
From my expirience, the first ballade is the most difficult to perform, although the fourth is probably technically more difficult and an extremly complex piece (especially all those polyphonic passages). There's a chance i will never perform the first although i have worked on it. I have heard it played bad too often (often becoming pitiful to watch) because of the coda. It's not particularly difficult, but everybody is going into the panic-mode there (and i'm sure i would too). If you know you can handle this kind of pressure, work on it.
But i'm absolutely serious about what i wrote above and i'm sure many pianists here can approve this. I love this piece and i would love to play it in public, but i just won't, because of that fact.
If you like the pieces i mentioned at the beginning, i would really consider playing one of them.
Looking at your repertoire, i would also suggest playing some other composers. You are thinking about playing some of the most difficult pieces in the common repertoire, but only have really worked on four different composers. Play some Haydn, a prelude and fugue by bach and something modern. Talk to your teacher about a well-balanced repertoire.