No one should be surprised (except for Mila, I guess, poor girl) I'm picking Nokdu but not for the kiss you all think.
For me this was the best kiss:
Why? Because when Nokdu kissed Dongju, he immediately felt she's not giving back, so he pulled away, not asking any questions. He knew something was wrong, he felt it and he did not push. This is a testament to his wonderful character.
Special mentions:
every other kiss in Nokdu.
