Agree with the comment above, it is much easier to learn something that you think you would enjoy. Personally, I would go for Beethoven's Pathetique (as I cannot stand Gershwin). I learned Beethoven Op. 13 about 3 or 4 years ago and found it fairly approachable - the 2nd and 3rd mvts are peasy, but the 1st requires some dedication and practice.
What is your level of repertoire?