Hmm, I think Beethoven and Schubert are quite a contrast to Chopin (especially Beethoven is), much more than Rachmaninov.
Well, I think that some later Beethoven and Schubert is very close to Chopin in style, but the early Beethoven especially is contrasting to Chopin. Problem is, I'm more fond of late Beethoven.
Schubert, I'm not really so familiar with his piano music as I am with his song cycles, though I know his impromptus.
And this elegy is one of the pieces where Rachmaninov comes the closest to Chopin.
I agree of course, but the Rachmaninoff prelude my teacher suggested was the Op. 23 No. 4 in D Major (she knew I would also choose something by Chopin), and I don't think that one is really any less similar to Chopin than the elegy. If I were playing a Chopin nocturne, I don't think I would also play the elegy, but I'm playing the 25/12 etude, which is a bit more contrasting to the elegy than a nocturne would be.
The main problem here is my own ignorance of piano repertoire - I have to like the stuff I'm playing, obviously, and I'm just not familiar with enough piano music to have a great deal to choose from. I'm reluctant to take others' suggestions on what I will like, too, and it usually takes repeated listening for me to warm up to a piece.
Anyway, that ignorance is something that I hope to lessen a bit through piano society (there is all sorts of music I don't know that is posted here), and I'm also taking a keyboard lit class this semester, with listening and reading assignments.
But for now, I can take advantage of the subjectiveness of "contrast" (it's totally dependent on my teacher's opinion).