Op.9, no.1 is my most favorite. The piece is really beautiful to hear, much more beautiful than Op.9, no.2 with its repetative theme.
Op.9, no.1 really soothes me after all that stress in driving lessons and practicing Chopin's 10/1 etude. Sometimes it does bring tears to my eyes- especially the middle section.

Followed by Nocturne Op.27, no.1- it's just as relaxing as 9/1. The coda is very beautiful to hear.

Then at 3rd place is Op.15, no.2- Makes me feel that I'm like in a 1st-class restaurant sitting in a table eating my favorite plate of 1 whole family-sized Roast Chicken, 3 cups of rice at night, but the feeling just disappears at the middle section, but thats alright. At least the theme comes back again.
I also like Nocturnes 9/3, 27/2, 48/1, and 55/2