stevensk
It's your opinion of which is the hardest of all Chopin. It's pretty subjective of which is the hardest of all Chopin.
IMO:
1. Rondo Op.16
2. Varations Op.2
3. Ballade Op.52
4. Etude Op.25 No.11
5. Sonata Op.58
6. Polonaise Op.44
7. Etude Op.25 No.6
8. Etude Op.10 No.2
9. Sonata Op.35
10. Ballade Op.38
11. Polonaise Op.53
12. Polonaise-Fantasie Op.61
13. Etude Op.25 No.12
14. Etude Op.25 No.10
15. Ballade Op.47
16. Ballade Op.23
17. Fantasy Op.49
18. Etude Op.10 No.4
19. Barcarolle Op.60
20. Nocturne Op. 48 No.1
21. Polonaise Op.22
21. Prelude Op.28 No.16
22. Nocturne Op.62 No.2
23. Nocturne Op.62 No.1
24. Sonata Op.4
And so on....
The reason I rate some Nocturnes higher than some Etudes and Preludes is because they're pretty long (5-7 minutes) and they're much harder than you think. All of the Etudes are generally harder, but it'll take longer to fully master the Nocturnes.
The list is pretty flawed; I made it up a few seconds ago

. I'll really like it if you guys edited it, because, like I said, it's a few seconds old. I think I made some things clear, like:
1. The 4th ballade isn't Chopin's hardest work
2. Nocturnes could be that hard
Looking back on the list, I realized that I put a Nocturnes before a Polonaise, and I put the 3rd Ballade before the 1st. Eh