The Devil. There are a few minor things I might have tweaked, but what it does structurally and thematically is extraordinary.
I like a lot of dramas but the perfect ones are: DREAM HIGH and WHO ARE YOU SCHOOL 2015, These two dramas are just the best for me!! :)
Nirvana in Fire ..everything about the drama is PERFECT!
@Sm3 i hear alot of people talk about nirvana in fire so i watched the first episode and it didnt catch my interest. does the story change or get better, just curious because the summary sounds very interesting.
@bandrew8964: The first 2 eps are kind of an introduction to the characters, so it was also quite confusing for me at the beginning! You just have to keep on watching... I think by ep 4 you'll know if you like it or not... But judging from your favorite list, I'm pretty sure you'll love it ;)
The only drama I've ever rated a 10/10 is It's Okay, That's Love 
I'm not a very harsh marker but I'll try and give u a compacted 10's list:

K-dramas:
- Gu Family Book
- You who came from the stars
- Moon that embraces the sun

C-dramas:
- Nirvana in Fire
- Prince of Lanling
- The Journey of Flower

Taiwanese:
- Autumn's concerto
I checked your list, I see you rated highly all dramas I liked as well.  Although it might be a pain, check up my list for more, cause I see a fairly similar taste, but these are some (although not all 10s) that I remember as the great ones (and haven't seen them on your list):
White Christmas (K)
Liar Game (J,K)
Bloody Monday (J)
I hear your voice (K)
Pinoccio (K)
Iljimae (K)
Time Between Dog and Wolf (K)
The Quiz Show (J)
Triangle (K)
Runaway Aisuru kimi no tame ni (J)
Here's my BIG list of dramas I find perfect from the first episode to the last one: http://mydramalist.com/list/q1Xzqdj3 <3 I wish there were more dramas like the ones I love <3
For me it has been Cruel City, Falling for Innocence, It's okay that's love, Healer, and Love me If you dare.
Tatta Hitotsu no Koi
The Princess Man
1L of Tears
Hana Yori Dango
Secret

my fav so far is Mask because their romance story is matured,
I haven't rated a drama 10/10 before because of personal opinion and reasons, but if I'll criticize a drama for perfection these come to mind:

Liar Game (K)  --->>  haven't watched the Japanese version, but the actors here are great.
Missing Noir M --->> I have a serious issue on the last episode.
Miss Ripley

Thanks everyone judging by the ones that come up the most these seem to be the one people like the most. Ill probably start with Nirvana in Fire and The Time Between Dog and Wolf. But the others seem pretty interesting as well.

Its Okay, Thats Love
White Christmas
Kill Me, Heal Me
Nirvana in Fire
The Time Between Dog and Wolf

Please post more, Im interesting in seeing if people have similar tastes with me.