What piano piece is harder? Chopin Nocturne in Db Mj or Chopin ballade no4

I am not so familiar with either piece, but I would say most likely the Ballade (though I am open to the idea that I might be wrong about this).

Unless your technique and musicianship are so well-developed that you can basically play anything, and what is easier or harder depends only on how well you personally connect with the music (i.e. mostly professionals), the Ballade is significantly harder by every measure I can think of...

Chopin Ballade No 4 seems fairly doable to start with but when listening sounds horribly difficult later on

Both pieces are difficult in their own ways. Overall, the ballade is certainly much more difficult though.
Regards,
Wurlz

The Ballade is by some way the hardest for me.