I started with Korea but i am mostly watching Japanese dramas these days.Also i recently started to watch Chinese dramas.
Not really a popular opinion here especially when everyone's watching Kdramas but I have to give my vote to Taiwan because they started everything thanks to Meteor Garden. I wouldn't even be in this website if I hadn't watched that.Though I must admit that their golden years of dramas have long been over and all their drama kings and queens have either moved to China for career growth or have settled down for good with their families. Then my love for Japanese and Chinese dramas probably come next and I don't think I'd ever venture into K or Thai dramas because all 3 countries that I just said have so much to offer and I don't even have enough time to watch them so what more if I become an open-minded drama watcher and watch Korean, Thai, etc. dramas lol. But this is one great discussion forum, I don't think anyone has started it before :D
Japan, Taiwan, China, Hong Kong
I started off watching mainly korean dramas and they soon start showing similar aspects in the dramas, you'll know what I mean once you start seeing a love triangle, hospital scene, someone rich doing something bad. But its not a bad thing, I do enjoy it, however I just watched the chinese dramas love o2o and love me if you dare and they were so good!! I'm planning on watching more chinese dramas, they are so unexpected and the romance scenes were A PLUS. 
Korea followed by Japan. 
South Korea > China > Japan > Taiwan
I am liking C-dramas right now. 

But still Korea is top!

Korea -> Japan -> China -> Taiwan
Japan, Taiwan, China, Hongkong, Thailand. :)
in most, romantic comedy genre of dramas I love Korean dramas. . in historical dramas I love Chinese  dramas. . . some action dramas from HK and some dramas from Taiwan . . . but mostly I watched between Korean dramas and Chinese dramas. . (that's all =D )
Right now,

China -> Korea-> TW-> Japan
South Korea followed by China. I rarely watch Japanese or Taiwanese Dramas...