TvN contents trend leader
TvN and JTBC are my favorites!!! Very high quality productions of drama and variety shows!

I probably only like KBS for the public channel.

MBC is my least. They have this boring vibe in their dramas that I can't stand. I do watch when it's my favorites' dramas. But they still really suck at editing.
1°) tvN
=> very good lately. Even when I don't love the drama, I like that they have unordinary plots.
=> favorite drama : Signal
2°) OCN
=> I didn't watch that many dramas but I have yet to find one boring.
=> Fav. drama : Bad Guys
3°) SBS
=> Good level overall
=> Fav dramas : I Hear Your Voice / Painter of the Wind
4°) MBC
=> Good level overall but slightly behind SBS
=> Fav. drama : Queen Seon Duk
5°) KBS2
=> Mainly for Period dramas. I often don't like the way they depict women in modern ones.
=> Fav. drama : Sungkyunkwan Scandal
Some of my favorites are from sbs, and I've seen really good ones from kbs and mbc too, but in terms of overall drama quality it definitely goes to tvn. They seem to have really well thought out, original and very realistic scripts/plots and I really enjoyed every single one I've watched so far. 
Why does everyone seem to forget about jTBC? They're probably my favorite, though they can be rather inconsistent. tvN is a close second. KBS probably produces the worst dramas, imo.
tvN has the drama's with different and interesting plots OCN follows it, but tvN is just the best for me at the moment
SBS, KBS2, MBC

I'm not into TVN / OCN / jTBC  dramas...
I've only recently started to pay attention to which drama airs on which network, and so far it seems that for Korean dramas - tvN, KBS2, MBC, jTBC, SBS - are the ones I prefer because each of them has 3 or more of my favorite dramas, soooo I'm liking them all, lol ^^ 
Together they offer dramas for all of my tastes - romance, action, tragedy, sageuks etc. I couldn't simply watch only one or two of those channels/networks because then my drama thirst would not be quenched
tvN certainly has a lot of original dramas, for me it's either I love them or hate them (when they go too overboard with the comedy, which is a genre I like only when done well and maturely; like I saw first 18 minutes of AMO and then had to turn it off bc neither I understood what's going on, nor I found the comedy well-done).

OCN certainly has a very unique genre, and I have really really enjoyed 2 out of 3 dramas of theirs I've seen.

I find jTBC dramas quite original, and I really quite enjoy them.

SBS and KBS2 have done lots of good dramas as well, which I really enjoyed. And SBS has done a lot I gave high ratings to, they also have the most dramas I put on my favorites list.

I think MBC is the lowest on my list because the amount of their dramas I've seen and the amount of dramas from them I've enjoyed doesn't make up good numbers, however they have W and I am in love with it, so that changes it a bit. ;D

So basically the order for me would be: SBS and OCN, then tvN and perhaps jTBC? or KBS2, and then MBC.
most dramas I have watched are either airing/aired in KBS or MBC. But tvN is catching up fast.
I never pay too much attention to stations, but looking over my favorite Korean dramas, it seems that I love KBS2 and MBC the most, though each has one drama I really didn't like.

MBC: W, Angry Mom, KMHM
KBS2: White Christmas, I Remember You, School 2015

There are some TVN and SBS dramas I've enjoyed as well, and loved Cruel City from jTBC.
1. TVn (Gold)  (their unique plot dramas are really interesting , The Best)
Favorites : Liar Game - Signal - Dear My Friend 

2. KBS2 (Silver) (their drama are usually very good) 
Favorites: Healer - White Christmas

3. MBC (Bronze) ( saguks, melodramas , well produced)
Favorites : Empress Ki - Two Weeks - Kill Me Heal Me


4. SBS (Carbon) (maybe a hit-or-miss, still most of my favorite dramas are from this channel - the most diverse, lots of genres)
Favorites: Six Flying Dragon - It's Okay That is Love - Mask

I have yet to watch an OCN drama, and I have seen only one drama from jTBC which I really loved (Age of Youth)
and one from KBS which was amazing (Secret).
I've noticed that some of the best dramas I've watched have been from tvN. I think followed by SBS