I don't really have a preference even though I've watched more korean stuff. I'm not gonna lie; korean people are more appealing to me. I was a huge fan of western stuff before (and still am, but I'm not into it now as much as I was back then) and korean dramas and movies are closer to the western culture (cinematography, acting.) than the japanese ones. I'm also a fan of k-pop (see avatar haha) and at the end of the day I'm just more enticed to watch korean dramas. That's pretty much it as for why there are more korean dramas on my drama list.
Korean dramas are great and somewhat addictive but they lack originality. If you watch a bunch of dramas of the same genre (and I'm going with the easy one here, romantic comedy), while the plot may not be the same, the plot twists give a feeling of déjà-vu. The only thing that makes it up for that is the cast (and therefore the couple's chemistry).
Japanese ones on the other hand, obviously have their flaws (the acting that comes off as overdone if you're not used to it and the cinematography is quite plain.) but they offer such a variety of choice and each japanese drama is unique in a way. They get risky and deep. You'll never get a
Majo no Jouken or
LIFE type of drama in Korea. If there is though, I'd bet it's not as greatly executed as the japanese one.
And obviously, the japanese dramas' biggest asset, their length. 40-50 minutes an episode on a 8-11 ep format is the best for any drama. Korean dramas need to sit down and realize that unnecessary and boring storylines/scenes really are unnecessary and boring.