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.