So I was trying to Google this, and the only thing that popped up was variations of "most beautiful Korean actresses." Thanks google, for letting us know how females are really valued. So, in your opinion, which actresses really bring the character to life? 

For me, I like:

Kim Hee Sun--I think she is able to show a wide range of emotions, as shown in Faith and Angry Mom. 

Han Groo--so, so funny! I like how she was able to take a sort-of typical lead girl and flesh her out. Like, I'm sure the writing was good too, but I felt like there were times another actress would have made the character stupid or irritating instead of funny and relatable. 

Bonus: Baek Jin Hee as the first empress in Empress Ki. You know a girl has talent when she takes a rather 2-dimensional villain and injects so much natural elegance that, even though I didn't like the character, I LOVED watching her onscreen. Really want this girl to get a lead role!

What are your thoughts? 

Although she didn't have a major role I loved Woo Hee Jin as Court Lady Oh in Moon Lovers. She had such a grace about her and as we got to know her character I couldn't help but appreciate her as an actress for having both a deep emotional side yet remaining so composed. ♡
Gong Hyo Jin, Ha Ji Won - I feel like these two are great actresses and you can really feel it when watching them onscreen.

Kim Seul Gi - she's fairly new but I really hope she gets more roles in the future, she's a really good actress.
Song Yi Kyu, Lee Yo Won and Ha Ji Won
From the dramas I've seen so far:

Hwang Jung Eum
- actually wasn't very impressed with her in Kill Me, Heal Me but in Secret she tore my heart out with her acting. Haven't seen her in anything else and personally I prefer watching her in tragic roles rather than comedic. Still, in her role (in Secret) I felt she gave it her all. 

Lee Bo Young
- her acting in God's Gift - 14 Days was what made me decide to give in to her other dramas of different genres. Really proved she could play a wide range of characters, and very well at that.

Han Ye Ri
- only saw her in Age of Youth but her acting was incredible. She barely had any lines but I still felt for her the most. Even with just subtle nods and glances, I was completely immersed in her character. Looking forward to seeing her (in) other dramas. 
Park Shin Hye- I know a lot of people won't agree with me, but I have always been really impressed with her, especially in Tree Of Heaven. She was only 16 at the time and I think she was wonderful.

Kim Sae Won- This girl is amazing! Even as a child actress, she was tackling serious roles and doing a better job than most adults. Acting just comes naturally to her.

Kim So Eun- She is just like the girl next door. Unlike a lot of other actresses, she always looks and acts so natural.

Kim Hee Sun is my favourite.  I really love her.  As you can tell from my profile pic, I love Kim Mi Kyung too.  and my third favourite is Kim Seul Gi.  They're my top 3 actors male or female :)  The thing that ties them all together is their comic timing as well as their versatility.
Yeah, KSH and Kim MI Kyung are awesome. I feel like KMK is like a stamp of approval..the dramas she chooses tend to be good (or at least have one good side character lol). And the chemistry KSH's been having with co-stars decades younger than her is scary good.  

You guys mentioned a lot of my other favorites too. I recently watched Ha Ji Won in The Time We Were Not In Love. It was my first time seeing he in a slice-of-life type drama and I thought she nailed it. 

Funny mentioning Hwang Jung Eum--this is going to sound terrible, but I had the hardest time getting into She Was Pretty and Secret because of her. When it comes to serious/melo stuff, she's pretty good, but her bubbly/Candy types come off as too shreiky and borderline hysterical (to me). I really wanted to watch Lucky Romance, but when I saw that she was the lead, I'm hesitant to try it. 

There were a few actresses mentioned that I'm not as familiar with, Song Yi Kyu and Le Yo Won. This gives me a way to find new good dramas hehe. 
AND, new question for everyone. What do you think contributes more to a good drama--the actor or the script?
I was reading an article about the "Big 3" vs. the cable channels, and their approaches. Basically, it seems like the Big 3 use big-name actors/actresses to draw the crowd in, while cable channels are using better-written, fresher scripts. Of course, just because the lead actor/actresses is famous, doesn't mean he/she is better at acting than a newbie, but the article just got me wondering ;) 
Lol I completely agree on what you said about Hwang Jung Eum's comedic acting. Couldn't get into Kill Me Heal Me due to (sort of the plot, but mainly) her characters bubbly personality. To me, she sounded like she was yelling all the time. After that one, it took me forever to decide to give Secret a go but only because it wasn't listed as comedy. Although I ended up loving her there, I don't plan to watch any of the well known comedy dramas from her anytime soon. 

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As for your question, (this was complicated one lol) obviously I believe both play a big factor when it comes to good dramas, but since you're asking about more, I'd have to go with acting because I feel it contributes directly TO the plot. For a good plot, you not only need good story but also believable characters. If the actor can't convince me, then I can't really connect to the story and immerse myself in it, regardless of how well written the drama is. Can you imagine your favorite drama being played by people who are "okay" at their role? *sobs* It would take all the magic away from it. On the other hand, if the plot is alright, but the acting is woah, the drama and people in it still get recognized for "so and so's great performance". What about you? :)
hmmm..for me its Choi Ji Woo.. ) 
Hmm, it's super complicated for me too. I agree with your points, especially because I feel most k-dramas tend to be character-driven. But at the same, I feel like a great actor can only do so much with a bad script. Maybe it depends on the genre too, I guess?

@Hanah and @eternalcities  For me the most important thing is the character and how they behave which directly points to writing.  I guess writing consistency really. I can deal with some plot holes but I can't deal with underdeveloped characters or characters who behave strangely.  Actors can enhance those characters and sometimes they can act them badly, but a really good character will live through that bad acting.  I'll give you an example.  I LOVED Signal.  absolutely loved it to bits.  but the lead actor had the same expression on his face the whole way through and it drove me nuts, but because his character, and the story were so well written they could withstand it, I still cared about him and what happened to him, I still loved the drama even though I thought the lead was wooden and weird.  

Then, there's the opposite, when excellent acting can't save ridiculous writing; my example is Missing You.  I quite like Yoo Seung Ho and Yoon Eun Hye, I have no doubt both of them are excellent actors but the writer and director just made them cry for the whole second half of the series.  Even though they're both really, really great at crying, I wanted to bang their heads together by the end of it and tell them to toughen up. Excellent acting could not save that drama for me.  The sad thing is the plot was great.  I just stopped caring about the characters because of the writing.
Gong Hyo Jin , ha Ji won and Choi Ji woo my top three best actress. Senior actresses I like Kim Mi Kyung and Kim Hae Sook. Newcomer I like Kim Seul Gi . I find these actresses  most natural in their acting and very convincing. There maybe more that I haven't watched much of their dramas yet .

i find Hwang jeung Eum over acting, yelling for no reasons - because of her, I couldn't watch KMHM after I have seen her in She was pretty.